enable lint prefer_single_quotes (#12665)

analysis_options.yaml

@@ -125,7 +125,7 @@ linter:
     # - prefer_interpolation_to_compose_strings # not yet tested
     - prefer_is_empty
     - prefer_is_not_empty
-    # - prefer_single_quote_strings # not yet tested
+    - prefer_single_quotes
     # - public_member_api_docs # this is the only difference from analysis_options_repo.yaml
     - recursive_getters
     - slash_for_doc_comments

analysis_options_repo.yaml

@@ -119,7 +119,7 @@ linter:
     # - prefer_interpolation_to_compose_strings # not yet tested
     - prefer_is_empty
     - prefer_is_not_empty
-    # - prefer_single_quote_strings # not yet tested
+    - prefer_single_quotes
     - public_member_api_docs # this is the only difference from analysis_options_repo.yaml
     - recursive_getters
     - slash_for_doc_comments

dev/automated_tests/flutter_test/filtering_test.dart

@@ -9,6 +9,6 @@ void main() {
     expect(2 + 2, 4);
   });
   test('excluded', () {
-    throw "this test should have been filtered out";
+    throw 'this test should have been filtered out';
   });
 }

dev/benchmarks/complex_layout/test_driver/semantics_perf_test.dart

@@ -31,7 +31,7 @@ void main() {
         expect(await driver.setSemantics(true), isTrue);
       });
 
-      final Iterable<TimelineEvent> semanticsEvents = timeline.events.where((TimelineEvent event) => event.name == "Semantics");
+      final Iterable<TimelineEvent> semanticsEvents = timeline.events.where((TimelineEvent event) => event.name == 'Semantics');
       if (semanticsEvents.length != 1)
         fail('Expected exactly one semantics event, got ${semanticsEvents.length}');
       final Duration semanticsTreeCreation = semanticsEvents.first.duration;

dev/manual_tests/lib/card_collection.dart

@@ -29,7 +29,7 @@ class CardCollectionState extends State<CardCollection> {
     const TextStyle(color: Colors.white, fontSize: 18.0, fontWeight: FontWeight.bold);
 
   // TODO(hansmuller): need a local image asset
-  static const String _sunshineURL = "http://www.walltor.com/images/wallpaper/good-morning-sunshine-58540.jpg";
+  static const String _sunshineURL = 'http://www.walltor.com/images/wallpaper/good-morning-sunshine-58540.jpg';
 
   static const double kCardMargins = 8.0;
   static const double kFixedCardHeight = 100.0;
@@ -103,23 +103,23 @@ class CardCollectionState extends State<CardCollection> {
         child: new ListView(
           children: <Widget>[
             const DrawerHeader(child: const Center(child: const Text('Options'))),
-            buildDrawerCheckbox("Make card labels editable", _editable, _toggleEditable),
-            buildDrawerCheckbox("Fixed size cards", _fixedSizeCards, _toggleFixedSizeCards),
-            buildDrawerCheckbox("Let the sun shine", _sunshine, _toggleSunshine),
-            buildDrawerCheckbox("Vary font sizes", _varyFontSizes, _toggleVaryFontSizes, enabled: !_editable),
+            buildDrawerCheckbox('Make card labels editable', _editable, _toggleEditable),
+            buildDrawerCheckbox('Fixed size cards', _fixedSizeCards, _toggleFixedSizeCards),
+            buildDrawerCheckbox('Let the sun shine', _sunshine, _toggleSunshine),
+            buildDrawerCheckbox('Vary font sizes', _varyFontSizes, _toggleVaryFontSizes, enabled: !_editable),
             const Divider(),
-            buildDrawerColorRadioItem("Deep Purple", Colors.deepPurple, _primaryColor, _selectColor),
-            buildDrawerColorRadioItem("Green", Colors.green, _primaryColor, _selectColor),
-            buildDrawerColorRadioItem("Amber", Colors.amber, _primaryColor, _selectColor),
-            buildDrawerColorRadioItem("Teal", Colors.teal, _primaryColor, _selectColor),
+            buildDrawerColorRadioItem('Deep Purple', Colors.deepPurple, _primaryColor, _selectColor),
+            buildDrawerColorRadioItem('Green', Colors.green, _primaryColor, _selectColor),
+            buildDrawerColorRadioItem('Amber', Colors.amber, _primaryColor, _selectColor),
+            buildDrawerColorRadioItem('Teal', Colors.teal, _primaryColor, _selectColor),
             const Divider(),
-            buildDrawerDirectionRadioItem("Dismiss horizontally", DismissDirection.horizontal, _dismissDirection, _changeDismissDirection, icon: Icons.code),
-            buildDrawerDirectionRadioItem("Dismiss left", DismissDirection.endToStart, _dismissDirection, _changeDismissDirection, icon: Icons.arrow_back),
-            buildDrawerDirectionRadioItem("Dismiss right", DismissDirection.startToEnd, _dismissDirection, _changeDismissDirection, icon: Icons.arrow_forward),
+            buildDrawerDirectionRadioItem('Dismiss horizontally', DismissDirection.horizontal, _dismissDirection, _changeDismissDirection, icon: Icons.code),
+            buildDrawerDirectionRadioItem('Dismiss left', DismissDirection.endToStart, _dismissDirection, _changeDismissDirection, icon: Icons.arrow_back),
+            buildDrawerDirectionRadioItem('Dismiss right', DismissDirection.startToEnd, _dismissDirection, _changeDismissDirection, icon: Icons.arrow_forward),
             const Divider(),
-            buildFontRadioItem("Left-align text", TextAlign.left, _textAlign, _changeTextAlign, icon: Icons.format_align_left, enabled: !_editable),
-            buildFontRadioItem("Center-align text", TextAlign.center, _textAlign, _changeTextAlign, icon: Icons.format_align_center, enabled: !_editable),
-            buildFontRadioItem("Right-align text", TextAlign.right, _textAlign, _changeTextAlign, icon: Icons.format_align_right, enabled: !_editable),
+            buildFontRadioItem('Left-align text', TextAlign.left, _textAlign, _changeTextAlign, icon: Icons.format_align_left, enabled: !_editable),
+            buildFontRadioItem('Center-align text', TextAlign.center, _textAlign, _changeTextAlign, icon: Icons.format_align_center, enabled: !_editable),
+            buildFontRadioItem('Right-align text', TextAlign.right, _textAlign, _changeTextAlign, icon: Icons.format_align_right, enabled: !_editable),
             const Divider(),
             new ListTile(
               leading: const Icon(Icons.dvr),
@@ -282,16 +282,16 @@ class CardCollectionState extends State<CardCollection> {
     String backgroundMessage;
     switch (_dismissDirection) {
       case DismissDirection.horizontal:
-        backgroundMessage = "Swipe in either direction";
+        backgroundMessage = 'Swipe in either direction';
         break;
       case DismissDirection.endToStart:
-        backgroundMessage = "Swipe left to dismiss";
+        backgroundMessage = 'Swipe left to dismiss';
         break;
       case DismissDirection.startToEnd:
-        backgroundMessage = "Swipe right to dismiss";
+        backgroundMessage = 'Swipe right to dismiss';
         break;
       default:
-        backgroundMessage = "Unsupported dismissDirection";
+        backgroundMessage = 'Unsupported dismissDirection';
     }
 
     // TODO(abarth): This icon is wrong in RTL.

dev/manual_tests/lib/material_arc.dart

@@ -211,7 +211,7 @@ class _PointDemoState extends State<_PointDemo> {
             child: new Padding(
               padding: const EdgeInsets.all(16.0),
               child: new Text(
-                "Tap the refresh button to run the animation. Drag the green "
+                'Tap the refresh button to run the animation. Drag the green '
                 "and red points to change the animation's path.",
                 style: Theme.of(context).textTheme.caption.copyWith(fontSize: 16.0)
               )
@@ -384,7 +384,7 @@ class _RectangleDemoState extends State<_RectangleDemo> {
             child: new Padding(
               padding: const EdgeInsets.all(16.0),
               child: new Text(
-                "Tap the refresh button to run the animation. Drag the rectangles "
+                'Tap the refresh button to run the animation. Drag the rectangles '
                 "to change the animation's path.",
                 style: Theme.of(context).textTheme.caption.copyWith(fontSize: 16.0)
               )

dev/manual_tests/lib/page_view.dart

@@ -112,7 +112,7 @@ class PageViewAppState extends State<PageViewApp> {
     return new AppBar(
       title: const Text('PageView'),
       actions: <Widget>[
-        new Text(scrollDirection == Axis.horizontal ? "horizontal" : "vertical"),
+        new Text(scrollDirection == Axis.horizontal ? 'horizontal' : 'vertical'),
       ],
     );
   }

dev/manual_tests/test/card_collection_test.dart

@@ -8,7 +8,7 @@ import 'package:flutter_test/flutter_test.dart';
 import '../lib/card_collection.dart' as card_collection;
 
 void main() {
-  testWidgets("Card Collection smoke test", (WidgetTester tester) async {
+  testWidgets('Card Collection smoke test', (WidgetTester tester) async {
     card_collection.main(); // builds the app and schedules a frame but doesn't trigger one
     await tester.pump(); // see https://github.com/flutter/flutter/issues/1865
     await tester.pump(); // triggers a frame

dev/manual_tests/test/color_testing_demo_test.dart

@@ -8,7 +8,7 @@ import 'package:flutter_test/flutter_test.dart';
 import '../lib/color_testing_demo.dart' as color_testing_demo;
 
 void main() {
-  testWidgets("Color testing demo smoke test", (WidgetTester tester) async {
+  testWidgets('Color testing demo smoke test', (WidgetTester tester) async {
     color_testing_demo.main(); // builds the app and schedules a frame but doesn't trigger one
     await tester.pump(); // see https://github.com/flutter/flutter/issues/1865
     await tester.pump(); // triggers a frame

dev/tools/gen_localizations.dart

@@ -42,34 +42,35 @@ const String outputHeader = '''
 final Map<String, Map<String, String>> localeToResources = <String, Map<String, String>>{};
 
 /// Maps locales to resource attributes.
-/// 
+///
 /// See also https://github.com/googlei18n/app-resource-bundle/wiki/ApplicationResourceBundleSpecification#resource-attributes
 final Map<String, Map<String, dynamic>> localeToResourceAttributes = <String, Map<String, dynamic>>{};
 
-// Return s as a Dart-parseable raw string in double quotes. Expand double quotes:
-// foo => r"foo"
-// foo "bar" => r"foo " '"' r"bar" '"'
+// Return s as a Dart-parseable raw string in single or double quotes. Expand double quotes:
+// foo => r'foo'
+// foo "bar" => r'foo "bar"'
+// foo 'bar' => r'foo ' "'" r'bar' "'"
 String generateString(String s) {
-  if (!s.contains('"'))
-    return 'r"$s"';
+  if (!s.contains("'"))
+    return "r'$s'";
 
   final StringBuffer output = new StringBuffer();
   bool started = false; // Have we started writing a raw string.
   for (int i = 0; i < s.length; i++) {
-    if (s[i] == '"') {
+    if (s[i] == "'") {
       if (started)
-        output.write('"');
-      output.write(' \'"\' ');
+        output.write("'");
+      output.write(' "\'" ');
       started = false;
     } else if (!started) {
-      output.write('r"${s[i]}');
+      output.write("r'${s[i]}");
       started = true;
     } else {
       output.write(s[i]);
     }
   }
   if (started)
-    output.write('"');
+    output.write("'");
   return output.toString();
 }
 
@@ -84,12 +85,12 @@ String generateLocalizationsMap() {
 const Map<String, Map<String, String>> localizations = const <String, Map<String, String>> {''');
 
   for (String locale in localeToResources.keys.toList()..sort()) {
-    output.writeln('  "$locale": const <String, String>{');
+    output.writeln("  '$locale': const <String, String>{");
 
     final Map<String, String> resources = localeToResources[locale];
     for (String name in resources.keys) {
       final String value = generateString(resources[name]);
-      output.writeln('    "$name": $value,');
+      output.writeln("    '$name': $value,");
     }
     output.writeln('  },');
   }

dev/tools/mega_gallery.dart

@@ -91,7 +91,7 @@ void _createEntry(File mainFile, int copies) {
 
   for (int i = 1; i < copies; i++) {
     imports.writeln("import 'gallery_$i/main.dart' as main_$i;");
-    importRefs.writeln("  main_$i.main;");
+    importRefs.writeln('  main_$i.main;');
   }
 
   final String contents = '''

examples/catalog/bin/sample_page.dart

@@ -57,7 +57,7 @@ String expandTemplate(String template, Map<String, String> values) {
     if (match.groupCount != 1)
       throw new SampleError('bad template keyword $match[0]');
     final String keyword = match[1];
-    return (values[keyword] ?? "");
+    return (values[keyword] ?? '');
   });
 }
 

examples/catalog/test/animated_list_test.dart

@@ -8,7 +8,7 @@ import 'package:flutter_test/flutter_test.dart';
 import '../lib/animated_list.dart' as animated_list_sample;
 
 void main() {
-  testWidgets("animated_list sample app smoke test", (WidgetTester tester) async {
+  testWidgets('animated_list sample app smoke test', (WidgetTester tester) async {
     animated_list_sample.main();
     await tester.pump();
 

examples/catalog/test/basic_app_bar_test.dart

@@ -20,7 +20,7 @@ Finder findChoiceCard(IconData icon) {
 }
 
 void main() {
-  testWidgets("basic_app_bar sample smoke test", (WidgetTester tester) async {
+  testWidgets('basic_app_bar sample smoke test', (WidgetTester tester) async {
     basic_app_bar_sample.main();
     await tester.pump();
 

examples/catalog/test/expansion_tile_sample_test.dart

@@ -9,7 +9,7 @@ import '../lib/expansion_tile_sample.dart' as expansion_tile_sample;
 import '../lib/expansion_tile_sample.dart' show Entry;
 
 void main() {
-  testWidgets("expansion_tile sample smoke test", (WidgetTester tester) async {
+  testWidgets('expansion_tile sample smoke test', (WidgetTester tester) async {
     expansion_tile_sample.main();
     await tester.pump();
 

examples/catalog/test/tabbed_app_bar_test.dart

@@ -19,7 +19,7 @@ Finder findTab(IconData icon) {
 }
 
 void main() {
-  testWidgets("tabbed_app_bar sample smoke test", (WidgetTester tester) async {
+  testWidgets('tabbed_app_bar sample smoke test', (WidgetTester tester) async {
     tabbed_app_bar_sample.main();
     await tester.pump();
 

examples/flutter_gallery/lib/demo/material/dialog_demo.dart

@@ -13,11 +13,11 @@ enum DialogDemoAction {
   agree,
 }
 
-const String _alertWithoutTitleText = "Discard draft?";
+const String _alertWithoutTitleText = 'Discard draft?';
 
 const String _alertWithTitleText =
-  "Let Google help apps determine location. This means sending anyonmous location "
-  "data to Google, even when no apps are running.";
+  'Let Google help apps determine location. This means sending anyonmous location '
+  'data to Google, even when no apps are running.';
 
 class DialogDemoItem extends StatelessWidget {
   const DialogDemoItem({ Key key, this.icon, this.color, this.text, this.onPressed }) : super(key: key);

examples/flutter_gallery/lib/demo/material/expansion_panels_demo.dart

@@ -225,7 +225,7 @@ class _ExpansionPanelsDemoState extends State<ExpasionPanelsDemo> {
         name: 'Location',
         value: _Location.Bahamas,
         hint: 'Select location',
-        valueToString: (_Location location) => location.toString().split(".")[1],
+        valueToString: (_Location location) => location.toString().split('.')[1],
         builder: (DemoItem<_Location> item) {
           void close() {
             setState(() {

examples/flutter_gallery/lib/demo/material/list_demo.dart

@@ -172,10 +172,10 @@ class _ListDemoState extends State<ListDemo> {
   Widget buildListTile(BuildContext context, String item) {
     Widget secondary;
     if (_itemType == _MaterialListType.twoLine) {
-      secondary = const Text("Additional item information.");
+      secondary = const Text('Additional item information.');
     } else if (_itemType == _MaterialListType.threeLine) {
       secondary = const Text(
-        "Even more additional list item information appears on line three.",
+        'Even more additional list item information appears on line three.',
       );
     }
     return new MergeSemantics(
@@ -192,7 +192,7 @@ class _ListDemoState extends State<ListDemo> {
 
   @override
   Widget build(BuildContext context) {
-    final String layoutText = _dense ? " \u2013 Dense" : "";
+    final String layoutText = _dense ? ' \u2013 Dense' : '';
     String itemTypeText;
     switch (_itemType) {
       case _MaterialListType.oneLine:

examples/flutter_gallery/lib/demo/material/overscroll_demo.dart

@@ -29,7 +29,7 @@ class OverscrollDemoState extends State<OverscrollDemo> {
     new Timer(const Duration(seconds: 3), () { completer.complete(null); });
     return completer.future.then((_) {
        _scaffoldKey.currentState?.showSnackBar(new SnackBar(
-         content: const Text("Refresh complete"),
+         content: const Text('Refresh complete'),
          action: new SnackBarAction(
            label: 'RETRY',
            onPressed: () {

examples/flutter_gallery/lib/demo/material/selection_controls_demo.dart

@@ -7,21 +7,21 @@ import 'package:flutter/material.dart';
 import '../../gallery/demo.dart';
 
 const String _checkboxText =
-  "Checkboxes allow the user to select multiple options from a set.";
+  'Checkboxes allow the user to select multiple options from a set.';
 
 const String _checkboxCode = 'selectioncontrols_checkbox';
 
 const String _radioText =
-  "Radio buttons allow the user to select one option from a set. Use radio "
-  "buttons for exclusive selection if you think that the user needs to see "
-  "all available options side-by-side.";
+  'Radio buttons allow the user to select one option from a set. Use radio '
+  'buttons for exclusive selection if you think that the user needs to see '
+  'all available options side-by-side.';
 
 const String _radioCode = 'selectioncontrols_radio';
 
 const String _switchText =
-  "On/off switches toggle the state of a single settings option. The option "
-  "that the switch controls, as well as the state it’s in, should be made "
-  "clear from the corresponding inline label.";
+  'On/off switches toggle the state of a single settings option. The option '
+  'that the switch controls, as well as the state it’s in, should be made '
+  'clear from the corresponding inline label.';
 
 const String _switchCode = 'selectioncontrols_switch';
 
@@ -37,19 +37,19 @@ class _SelectionControlsDemoState extends State<SelectionControlsDemo> {
   Widget build(BuildContext context) {
     final List<ComponentDemoTabData> demos = <ComponentDemoTabData>[
       new ComponentDemoTabData(
-        tabName: "CHECKBOX",
+        tabName: 'CHECKBOX',
         description: _checkboxText,
         demoWidget: buildCheckbox(),
         exampleCodeTag: _checkboxCode
       ),
       new ComponentDemoTabData(
-        tabName: "RADIO",
+        tabName: 'RADIO',
         description: _radioText,
         demoWidget: buildRadio(),
         exampleCodeTag: _radioCode
       ),
       new ComponentDemoTabData(
-        tabName: "SWITCH",
+        tabName: 'SWITCH',
         description: _switchText,
         demoWidget: buildSwitch(),
         exampleCodeTag: _switchCode

examples/flutter_gallery/lib/demo/material/snack_bar_demo.dart

@@ -5,16 +5,16 @@
 import 'package:flutter/material.dart';
 
 const String _text1 =
-  "Snackbars provide lightweight feedback about an operation by "
-  "showing a brief message at the bottom of the screen. Snackbars "
-  "can contain an action.";
+  'Snackbars provide lightweight feedback about an operation by '
+  'showing a brief message at the bottom of the screen. Snackbars '
+  'can contain an action.';
 
 const String _text2 =
-  "Snackbars should contain a single line of text directly related "
-  "to the operation performed. They cannot contain icons.";
+  'Snackbars should contain a single line of text directly related '
+  'to the operation performed. They cannot contain icons.';
 
 const String _text3 =
-  "By default snackbars automatically disappear after a few seconds ";
+  'By default snackbars automatically disappear after a few seconds ';
 
 class SnackBarDemo extends StatefulWidget {
   const SnackBarDemo({ Key key }) : super(key: key);

examples/flutter_gallery/lib/demo/material/tabs_fab_demo.dart

@@ -6,9 +6,9 @@ import 'package:flutter/material.dart';
 
 const String _explanatoryText =
   "When the Scaffold's floating action button changes, the new button fades and "
-  "turns into view. In this demo, changing tabs can cause the app to be rebuilt "
-  "with a FloatingActionButton that the Scaffold distinguishes from the others "
-  "by its key.";
+  'turns into view. In this demo, changing tabs can cause the app to be rebuilt '
+  'with a FloatingActionButton that the Scaffold distinguishes from the others '
+  'by its key.';
 
 class _Page {
   _Page({ this.label, this.colors, this.icon });

examples/flutter_gallery/lib/demo/material/tooltip_demo.dart

@@ -5,9 +5,9 @@
 import 'package:flutter/material.dart';
 
 const String _introText =
-  "Tooltips are short identifying messages that briefly appear in response to "
-  "a long press. Tooltip messages are also used by services that make Flutter "
-  "apps accessible, like screen readers.";
+  'Tooltips are short identifying messages that briefly appear in response to '
+  'a long press. Tooltip messages are also used by services that make Flutter '
+  'apps accessible, like screen readers.';
 
 class TooltipDemo extends StatelessWidget {
 

examples/flutter_gallery/lib/demo/pesto_demo.dart

@@ -162,14 +162,14 @@ class _RecipeGridPageState extends State<RecipeGridPage> {
 
   void showFavoritesPage(BuildContext context) {
     Navigator.push(context, new MaterialPageRoute<Null>(
-      settings: const RouteSettings(name: "/pesto/favorites"),
+      settings: const RouteSettings(name: '/pesto/favorites'),
       builder: (BuildContext context) => new PestoFavorites(),
     ));
   }
 
   void showRecipePage(BuildContext context, Recipe recipe) {
     Navigator.push(context, new MaterialPageRoute<Null>(
-      settings: const RouteSettings(name: "/pesto/recipe"),
+      settings: const RouteSettings(name: '/pesto/recipe'),
       builder: (BuildContext context) {
         return new Theme(
           data: _kTheme.copyWith(platform: Theme.of(context).platform),

examples/flutter_gallery/lib/gallery/syntax_highlighter.dart

@@ -118,10 +118,10 @@ class DartSyntaxHighlighter extends SyntaxHighlighter {
 
     while (!_scanner.isDone) {
       // Skip White space
-      _scanner.scan(new RegExp(r"\s+"));
+      _scanner.scan(new RegExp(r'\s+'));
 
       // Block comments
-      if (_scanner.scan(new RegExp(r"/\*(.|\n)*\*/"))) {
+      if (_scanner.scan(new RegExp(r'/\*(.|\n)*\*/'))) {
         _spans.add(new _HighlightSpan(
           _HighlightType.comment,
           _scanner.lastMatch.start,
@@ -131,12 +131,12 @@ class DartSyntaxHighlighter extends SyntaxHighlighter {
       }
 
       // Line comments
-      if (_scanner.scan("//")) {
+      if (_scanner.scan('//')) {
         final int startComment = _scanner.lastMatch.start;
 
         bool eof = false;
         int endComment;
-        if (_scanner.scan(new RegExp(r".*\n"))) {
+        if (_scanner.scan(new RegExp(r'.*\n'))) {
           endComment = _scanner.lastMatch.end - 1;
         } else {
           eof = true;
@@ -216,7 +216,7 @@ class DartSyntaxHighlighter extends SyntaxHighlighter {
       }
 
       // Double
-      if (_scanner.scan(new RegExp(r"\d+\.\d+"))) {
+      if (_scanner.scan(new RegExp(r'\d+\.\d+'))) {
         _spans.add(new _HighlightSpan(
           _HighlightType.number,
           _scanner.lastMatch.start,
@@ -226,7 +226,7 @@ class DartSyntaxHighlighter extends SyntaxHighlighter {
       }
 
       // Integer
-      if (_scanner.scan(new RegExp(r"\d+"))) {
+      if (_scanner.scan(new RegExp(r'\d+'))) {
         _spans.add(new _HighlightSpan(
           _HighlightType.number,
           _scanner.lastMatch.start,
@@ -236,7 +236,7 @@ class DartSyntaxHighlighter extends SyntaxHighlighter {
       }
 
       // Punctuation
-      if (_scanner.scan(new RegExp(r"[\[\]{}().!=<>&\|\?\+\-\*/%\^~;:,]"))) {
+      if (_scanner.scan(new RegExp(r'[\[\]{}().!=<>&\|\?\+\-\*/%\^~;:,]'))) {
         _spans.add(new _HighlightSpan(
           _HighlightType.punctuation,
           _scanner.lastMatch.start,
@@ -246,7 +246,7 @@ class DartSyntaxHighlighter extends SyntaxHighlighter {
       }
 
       // Meta data
-      if (_scanner.scan(new RegExp(r"@\w+"))) {
+      if (_scanner.scan(new RegExp(r'@\w+'))) {
         _spans.add(new _HighlightSpan(
           _HighlightType.keyword,
           _scanner.lastMatch.start,
@@ -256,11 +256,11 @@ class DartSyntaxHighlighter extends SyntaxHighlighter {
       }
 
       // Words
-      if (_scanner.scan(new RegExp(r"\w+"))) {
+      if (_scanner.scan(new RegExp(r'\w+'))) {
         _HighlightType type;
 
         String word = _scanner.lastMatch[0];
-        if (word.startsWith("_"))
+        if (word.startsWith('_'))
           word = word.substring(1);
 
         if (_kKeywords.contains(word))
@@ -269,7 +269,7 @@ class DartSyntaxHighlighter extends SyntaxHighlighter {
           type = _HighlightType.keyword;
         else if (_firstLetterIsUpperCase(word))
           type = _HighlightType.klass;
-        else if (word.length >= 2 && word.startsWith("k") && _firstLetterIsUpperCase(word.substring(1)))
+        else if (word.length >= 2 && word.startsWith('k') && _firstLetterIsUpperCase(word.substring(1)))
           type = _HighlightType.constant;
 
         if (type != null) {

examples/flutter_gallery/test/calculator/logic.dart

@@ -16,7 +16,7 @@ void main() {
     expression = expression.appendDigit(4);
     expression = expression.computeResult();
     expect(expression.state, equals(ExpressionState.Result));
-    expect(expression.toString(), equals("24"));
+    expect(expression.toString(), equals('24'));
   });
 
   test('Test floating point 0.1 + 0.2 = 0.3', () {
@@ -30,7 +30,7 @@ void main() {
     expression = expression.appendDigit(2);
     expression = expression.computeResult();
     expect(expression.state, equals(ExpressionState.Result));
-    expect(expression.toString(), equals("0.3"));
+    expect(expression.toString(), equals('0.3'));
   });
 
   test('Test floating point 1.0/10.0 = 0.1', () {
@@ -45,7 +45,7 @@ void main() {
     expression = expression.appendDigit(0);
     expression = expression.computeResult();
     expect(expression.state, equals(ExpressionState.Result));
-    expect(expression.toString(), equals("0.1"));
+    expect(expression.toString(), equals('0.1'));
   });
 
   test('Test 1/0 = Infinity', () {
@@ -55,7 +55,7 @@ void main() {
     expression = expression.appendDigit(0);
     expression = expression.computeResult();
     expect(expression.state, equals(ExpressionState.Result));
-    expect(expression.toString(), equals("Infinity"));
+    expect(expression.toString(), equals('Infinity'));
   });
 
   test('Test use result in next calculation: 1 + 1 = 2 + 1 = 3 + 1 = 4', () {
@@ -71,7 +71,7 @@ void main() {
     expression = expression.appendDigit(1);
     expression = expression.computeResult();
     expect(expression.state, equals(ExpressionState.Result));
-    expect(expression.toString(), equals("4"));
+    expect(expression.toString(), equals('4'));
   });
 
   test('Test minus -3 - -2 = -1', () {
@@ -83,6 +83,6 @@ void main() {
     expression = expression.appendDigit(2);
     expression = expression.computeResult();
     expect(expression.state, equals(ExpressionState.Result));
-    expect(expression.toString(), equals("-1"));
+    expect(expression.toString(), equals('-1'));
   });
 }

examples/flutter_gallery/test/drawer_test.dart

@@ -51,21 +51,21 @@ void main() {
     expect(app.theme.platform, equals(TargetPlatform.iOS));
 
     // Verify the font scale.
-    final Size origTextSize = tester.getSize(find.text("Small"));
+    final Size origTextSize = tester.getSize(find.text('Small'));
     expect(origTextSize, equals(const Size(176.0, 14.0)));
 
     // Switch font scale.
     await tester.tap(find.text('Small'));
     await tester.pump();
     await tester.pump(const Duration(seconds: 1)); // Wait until it's changed.
-    final Size textSize = tester.getSize(find.text("Small"));
+    final Size textSize = tester.getSize(find.text('Small'));
     expect(textSize, equals(const Size(176.0, 11.0)));
 
     // Set font scale back to default.
     await tester.tap(find.text('System Default'));
     await tester.pump();
     await tester.pump(const Duration(seconds: 1)); // Wait until it's changed.
-    final Size newTextSize = tester.getSize(find.text("Small"));
+    final Size newTextSize = tester.getSize(find.text('Small'));
     expect(newTextSize, equals(origTextSize));
 
     // Scroll to the bottom of the menu.

examples/flutter_gallery/test/example_code_parser_test.dart

@@ -21,7 +21,7 @@ void main() {
   });
 }
 
-const String testCodeFile = """// A fake test file
+const String testCodeFile = '''// A fake test file
 // START test_0
 test 0 0
 test 0 1
@@ -32,7 +32,7 @@ test 0 1
 test 1 0
 test 1 1
 // END
-""";
+''';
 
 class TestAssetBundle extends AssetBundle {
   @override

examples/flutter_view/lib/main.dart

@@ -26,9 +26,9 @@ class MyHomePage extends StatefulWidget {
 }
 
 class _MyHomePageState extends State<MyHomePage> {
-  static const String _channel = "increment";
-  static const String _pong = "pong";
-  static const String _emptyMessage = "";
+  static const String _channel = 'increment';
+  static const String _pong = 'pong';
+  static const String _emptyMessage = '';
   static const BasicMessageChannel<String> platform =
       const BasicMessageChannel<String>(_channel, const StringCodec());
 

examples/hello_world/test/hello_test.dart

@@ -7,7 +7,7 @@ import 'package:flutter_test/flutter_test.dart';
 import '../lib/main.dart' as hello_world;
 
 void main() {
-  testWidgets("Hello world smoke test", (WidgetTester tester) async {
+  testWidgets('Hello world smoke test', (WidgetTester tester) async {
     hello_world.main(); // builds the app and schedules a frame but doesn't trigger one
     await tester.pump(); // triggers a frame
 

examples/layers/rendering/touch_input.dart

@@ -104,7 +104,7 @@ void main() {
   final RenderParagraph paragraph = new RenderParagraph(
     const TextSpan(
       style: const TextStyle(color: Colors.black87),
-      text: "Touch me!",
+      text: 'Touch me!',
     ),
     textDirection: TextDirection.ltr,
   );

examples/layers/services/isolate.dart

@@ -46,21 +46,21 @@ class Calculator {
     try {
       final List<dynamic> result = decoder.convert(_data);
       final int n = result.length;
-      onResultListener("Decoded $n results");
+      onResultListener('Decoded $n results');
     } catch (e, stack) {
-      print("Invalid JSON file: $e");
+      print('Invalid JSON file: $e');
       print(stack);
     }
   }
 
   static String _replicateJson(String data, int count) {
-    final StringBuffer buffer = new StringBuffer()..write("[");
+    final StringBuffer buffer = new StringBuffer()..write('[');
     for (int i = 0; i < count; i++) {
       buffer.write(data);
       if (i < count - 1)
         buffer.write(',');
     }
-    buffer.write("]");
+    buffer.write(']');
     return buffer.toString();
   }
 }

examples/layers/widgets/styled_text.dart

@@ -24,7 +24,7 @@ final List<List<String>> _kNameLines = _kDialogText
   .toList();
 
 final TextStyle _kDaveStyle = new TextStyle(color: Colors.indigo.shade400, height: 1.8);
-final TextStyle _kHalStyle = new TextStyle(color: Colors.red.shade400, fontFamily: "monospace");
+final TextStyle _kHalStyle = new TextStyle(color: Colors.red.shade400, fontFamily: 'monospace');
 final TextStyle _kBold = const TextStyle(fontWeight: FontWeight.bold);
 final TextStyle _kUnderline = const TextStyle(
   decoration: TextDecoration.underline,
@@ -33,7 +33,7 @@ final TextStyle _kUnderline = const TextStyle(
 );
 
 Widget toStyledText(String name, String text) {
-  final TextStyle lineStyle = (name == "Dave") ? _kDaveStyle : _kHalStyle;
+  final TextStyle lineStyle = (name == 'Dave') ? _kDaveStyle : _kHalStyle;
   return new RichText(
     key: new Key(text),
     text: new TextSpan(
@@ -55,7 +55,7 @@ Widget toStyledText(String name, String text) {
   );
 }
 
-Widget toPlainText(String name, String text) => new Text(name + ":" + text);
+Widget toPlainText(String name, String text) => new Text(name + ':' + text);
 
 class SpeakerSeparator extends StatelessWidget {
   @override

examples/platform_channel/lib/main.dart

@@ -27,7 +27,7 @@ class _PlatformChannelState extends State<PlatformChannel> {
       final int result = await methodChannel.invokeMethod('getBatteryLevel');
       batteryLevel = 'Battery level: $result%.';
     } on PlatformException {
-      batteryLevel = "Failed to get battery level.";
+      batteryLevel = 'Failed to get battery level.';
     }
     setState(() {
       _batteryLevel = batteryLevel;
@@ -49,7 +49,7 @@ class _PlatformChannelState extends State<PlatformChannel> {
 
   void _onError(PlatformException error) {
     setState(() {
-      _chargingStatus = "Battery status: unknown.";
+      _chargingStatus = 'Battery status: unknown.';
     });
   }
 

examples/platform_channel_swift/lib/main.dart

@@ -27,7 +27,7 @@ class _PlatformChannelState extends State<PlatformChannel> {
       final int result = await methodChannel.invokeMethod('getBatteryLevel');
       batteryLevel = 'Battery level: $result%.';
     } on PlatformException {
-      batteryLevel = "Failed to get battery level.";
+      batteryLevel = 'Failed to get battery level.';
     }
     setState(() {
       _batteryLevel = batteryLevel;
@@ -49,7 +49,7 @@ class _PlatformChannelState extends State<PlatformChannel> {
 
   void _onError(PlatformException error) {
     setState(() {
-      _chargingStatus = "Battery status: unknown.";
+      _chargingStatus = 'Battery status: unknown.';
     });
   }
 

examples/platform_view/lib/main.dart

@@ -35,7 +35,7 @@ class MyHomePage extends StatefulWidget {
 
 class _MyHomePageState extends State<MyHomePage> {
   static const MethodChannel _methodChannel =
-      const MethodChannel("samples.flutter.io/platform_view");
+      const MethodChannel('samples.flutter.io/platform_view');
 
   int _counter = 0;
 
@@ -47,7 +47,7 @@ class _MyHomePageState extends State<MyHomePage> {
 
   Future<Null> _launchPlatformCount() async {
     final int platformCounter =
-        await _methodChannel.invokeMethod("switchView", _counter);
+        await _methodChannel.invokeMethod('switchView', _counter);
     setState(() {
       _counter = platformCounter;
     });

examples/stocks/lib/stock_home.dart

@@ -245,9 +245,9 @@ class StockHomeState extends State<StockHome> {
       stock.lastSale += 1.0;
     });
     _scaffoldKey.currentState.showSnackBar(new SnackBar(
-      content: new Text("Purchased ${stock.symbol} for ${stock.lastSale}"),
+      content: new Text('Purchased ${stock.symbol} for ${stock.lastSale}'),
       action: new SnackBarAction(
-        label: "BUY MORE",
+        label: 'BUY MORE',
         onPressed: () {
           _buyStock(stock);
         },
@@ -278,7 +278,7 @@ class StockHomeState extends State<StockHome> {
     );
   }
 
-  static const List<String> portfolioSymbols = const <String>["AAPL","FIZZ", "FIVE", "FLAT", "ZINC", "ZNGA"];
+  static const List<String> portfolioSymbols = const <String>['AAPL','FIZZ', 'FIVE', 'FLAT', 'ZINC', 'ZNGA'];
 
   Widget buildSearchBar() {
     return new AppBar(

examples/stocks/lib/stock_row.dart

@@ -30,10 +30,10 @@ class StockRow extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final String lastSale = "\$${stock.lastSale.toStringAsFixed(2)}";
-    String changeInPrice = "${stock.percentChange.toStringAsFixed(2)}%";
+    final String lastSale = '\$${stock.lastSale.toStringAsFixed(2)}';
+    String changeInPrice = '${stock.percentChange.toStringAsFixed(2)}%';
     if (stock.percentChange > 0)
-      changeInPrice = "+" + changeInPrice;
+      changeInPrice = '+' + changeInPrice;
     return new InkWell(
       onTap: _getHandler(onPressed),
       onDoubleTap: _getHandler(onDoubleTap),

examples/stocks/lib/stock_settings.dart

@@ -68,8 +68,8 @@ class StockSettingsState extends State<StockSettings> {
         showDialog<bool>(
           context: context,
           child: new AlertDialog(
-            title: const Text("Change mode?"),
-            content: const Text("Optimistic mode means everything is awesome. Are you sure you can handle that?"),
+            title: const Text('Change mode?'),
+            content: const Text('Optimistic mode means everything is awesome. Are you sure you can handle that?'),
             actions: <Widget>[
               new FlatButton(
                 child: const Text('NO THANKS'),

examples/stocks/lib/stock_symbol_viewer.dart

@@ -16,10 +16,10 @@ class _StockSymbolView extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     assert(stock != null);
-    final String lastSale = "\$${stock.lastSale.toStringAsFixed(2)}";
-    String changeInPrice = "${stock.percentChange.toStringAsFixed(2)}%";
+    final String lastSale = '\$${stock.lastSale.toStringAsFixed(2)}';
+    String changeInPrice = '${stock.percentChange.toStringAsFixed(2)}%';
     if (stock.percentChange > 0)
-      changeInPrice = "+" + changeInPrice;
+      changeInPrice = '+' + changeInPrice;
 
     final TextStyle headings = Theme.of(context).textTheme.body2;
     return new Container(

packages/flutter/lib/src/foundation/profile.dart

@@ -5,7 +5,7 @@
 import 'dart:ui';
 
 /// Whether we've been built in release mode.
-const bool _kReleaseMode = const bool.fromEnvironment("dart.vm.product");
+const bool _kReleaseMode = const bool.fromEnvironment('dart.vm.product');
 
 /// When running in profile mode (or debug mode), invoke the given function.
 ///

packages/flutter/lib/src/painting/colors.dart

@@ -170,7 +170,7 @@ class HSVColor {
   int get hashCode => hashValues(alpha, hue, saturation, value);
 
   @override
-  String toString() => "HSVColor($alpha, $hue, $saturation, $value)";
+  String toString() => 'HSVColor($alpha, $hue, $saturation, $value)';
 }
 
 /// A color that has a small table of related colors called a "swatch".

packages/flutter/lib/src/rendering/sliver_multi_box_adaptor.dart

@@ -578,7 +578,7 @@ abstract class RenderSliverMultiBoxAdaptor extends RenderSliver
       RenderBox child = firstChild;
       while (true) {
         final SliverMultiBoxAdaptorParentData childParentData = child.parentData;
-        children.add(child.toDiagnosticsNode(name: "child with index ${childParentData.index}"));
+        children.add(child.toDiagnosticsNode(name: 'child with index ${childParentData.index}'));
         if (child == lastChild)
           break;
         child = childParentData.nextSibling;
@@ -588,7 +588,7 @@ abstract class RenderSliverMultiBoxAdaptor extends RenderSliver
       final List<int> indices = _keepAliveBucket.keys.toList()..sort();
       for (int index in indices) {
         children.add(_keepAliveBucket[index].toDiagnosticsNode(
-          name: "child with index $index (kept alive offstage)",
+          name: 'child with index $index (kept alive offstage)',
           style: DiagnosticsTreeStyle.offstage,
         ));
       }

packages/flutter/lib/src/rendering/stack.dart

@@ -134,7 +134,7 @@ class RelativeRect {
   int get hashCode => hashValues(left, top, right, bottom);
 
   @override
-  String toString() => "RelativeRect.fromLTRB(${left?.toStringAsFixed(1)}, ${top?.toStringAsFixed(1)}, ${right?.toStringAsFixed(1)}, ${bottom?.toStringAsFixed(1)})";
+  String toString() => 'RelativeRect.fromLTRB(${left?.toStringAsFixed(1)}, ${top?.toStringAsFixed(1)}, ${right?.toStringAsFixed(1)}, ${bottom?.toStringAsFixed(1)})';
 }
 
 /// Parent data for use with [RenderStack].

packages/flutter/lib/src/rendering/table.dart

@@ -1167,7 +1167,7 @@ class RenderTable extends RenderBox {
     description.add(new DiagnosticsProperty<TableColumnWidth>('default column width', defaultColumnWidth));
     description.add(new MessageProperty('table size', '$columns\u00D7$rows'));
     description.add(new IterableProperty<double>('column offsets', _columnLefts, ifNull: 'unknown'));
-    description.add(new IterableProperty<double>('row offsets', _rowTops, ifNull: "unknown"));
+    description.add(new IterableProperty<double>('row offsets', _rowTops, ifNull: 'unknown'));
   }
 
   @override

packages/flutter/lib/src/services/image_resolution.dart

@@ -246,7 +246,7 @@ class AssetImage extends AssetBundleImageProvider {
       return candidates[lower];
   }
 
-  static final RegExp _extractRatioRegExp = new RegExp(r"/?(\d+(\.\d*)?)x/");
+  static final RegExp _extractRatioRegExp = new RegExp(r'/?(\d+(\.\d*)?)x/');
 
   double _parseScale(String key) {
     final Match match = _extractRatioRegExp.firstMatch(key);

packages/flutter/lib/src/services/platform_channel.dart

@@ -150,7 +150,7 @@ class MethodChannel {
       codec.encodeMethodCall(new MethodCall(method, arguments)),
     );
     if (result == null)
-      throw new MissingPluginException("No implementation found for method $method on channel $name");
+      throw new MissingPluginException('No implementation found for method $method on channel $name');
     return codec.decodeEnvelope(result);
   }
 

packages/flutter/lib/src/widgets/focus_manager.dart

@@ -367,7 +367,7 @@ class FocusScopeNode extends Object with DiagnosticableTreeMixin {
       FocusScopeNode child = _firstChild;
       int count = 1;
       while (true) {
-        children.add(child.toDiagnosticsNode(name: "child $count"));
+        children.add(child.toDiagnosticsNode(name: 'child $count'));
         if (child == _lastChild)
           break;
         child = child._nextSibling;

packages/flutter/lib/src/widgets/framework.dart

@@ -3833,7 +3833,7 @@ class ParentDataElement<T extends RenderObjectWidget> extends ProxyElement {
       throw new FlutterError(
         'Incorrect use of ParentDataWidget.\n' +
         widget.debugDescribeInvalidAncestorChain(
-          description: "$this",
+          description: '$this',
           ownershipChain: parent.debugGetCreatorChain(10),
           foundValidAncestor: ancestor != null,
           badAncestors: badAncestors

packages/flutter/test/material/expansion_panel_test.dart

@@ -71,7 +71,7 @@ void main() {
     box = tester.renderObject(find.byType(ExpansionPanelList));
     expect(box.size.height - oldHeight, greaterThanOrEqualTo(100.0)); // 100 + some margin
   });
-  testWidgets("Multiple Panel List test", (WidgetTester tester) async {
+  testWidgets('Multiple Panel List test', (WidgetTester tester) async {
     await tester.pumpWidget(
       new MaterialApp(
         home: new ListView(

packages/flutter/test/rendering/positioned_box_test.dart

@@ -16,8 +16,8 @@ void main() {
     final RenderPositionedBox positioner = new RenderPositionedBox(child: sizer);
     layout(positioner, constraints: new BoxConstraints.loose(const Size(200.0, 200.0)));
 
-    expect(positioner.size.width, equals(200.0), reason: "positioner width");
-    expect(positioner.size.height, equals(200.0), reason: "positioner height");
+    expect(positioner.size.width, equals(200.0), reason: 'positioner width');
+    expect(positioner.size.height, equals(200.0), reason: 'positioner height');
   });
 
   test('RenderPositionedBox shrink wraps', () {
@@ -28,21 +28,21 @@ void main() {
     final RenderPositionedBox positioner = new RenderPositionedBox(child: sizer, widthFactor: 1.0);
     layout(positioner, constraints: new BoxConstraints.loose(const Size(200.0, 200.0)));
 
-    expect(positioner.size.width, equals(100.0), reason: "positioner width");
-    expect(positioner.size.height, equals(200.0), reason: "positioner height");
+    expect(positioner.size.width, equals(100.0), reason: 'positioner width');
+    expect(positioner.size.height, equals(200.0), reason: 'positioner height');
 
     positioner.widthFactor = null;
     positioner.heightFactor = 1.0;
     pumpFrame();
 
-    expect(positioner.size.width, equals(200.0), reason: "positioner width");
-    expect(positioner.size.height, equals(100.0), reason: "positioner height");
+    expect(positioner.size.width, equals(200.0), reason: 'positioner width');
+    expect(positioner.size.height, equals(100.0), reason: 'positioner height');
 
     positioner.widthFactor = 1.0;
     pumpFrame();
 
-    expect(positioner.size.width, equals(100.0), reason: "positioner width");
-    expect(positioner.size.height, equals(100.0), reason: "positioner height");
+    expect(positioner.size.width, equals(100.0), reason: 'positioner width');
+    expect(positioner.size.height, equals(100.0), reason: 'positioner height');
   });
 
   test('RenderPositionedBox width and height factors', () {

packages/flutter/test/rendering/semantics_test.dart

@@ -208,7 +208,7 @@ void main() {
       ..addAction(SemanticsAction.showOnScreen, () { })
       ..isChecked = false
       ..isSelected = true
-      ..label = "Use all the properties"
+      ..label = 'Use all the properties'
       ..textDirection = TextDirection.rtl;
     final SemanticsNode allProperties = new SemanticsNode()
       ..rect = new Rect.fromLTWH(50.0, 10.0, 20.0, 30.0)

packages/flutter/test/scheduler/animation_test.dart

@@ -13,11 +13,11 @@ class TestSchedulerBinding extends BindingBase with SchedulerBinding { }
 void main() {
   final SchedulerBinding scheduler = new TestSchedulerBinding();
 
-  test("Check for a time dilation being in effect", () {
+  test('Check for a time dilation being in effect', () {
     expect(timeDilation, equals(1.0));
   });
 
-  test("Can cancel queued callback", () {
+  test('Can cancel queued callback', () {
     int secondId;
 
     bool firstCallbackRan = false;

packages/flutter_driver/lib/src/error.dart

@@ -96,7 +96,7 @@ class LogRecord {
   ///
   /// It is meant to be read by humans. There's no guarantee that this value is
   /// stable enough to be parsed by machines.
-  String get levelDescription => level.toString().split(".").last;
+  String get levelDescription => level.toString().split('.').last;
 
   @override
   String toString() => '[${levelDescription.padRight(5)}] $loggerName: $message';

packages/flutter_localizations/lib/src/material_localizations.dart

@@ -348,7 +348,7 @@ class GlobalMaterialLocalizations implements MaterialLocalizations {
 
   /// Looks up text geometry defined in [MaterialTextGeometry].
   @override
-  TextTheme get localTextGeometry => MaterialTextGeometry.forScriptCategory(_nameToValue["scriptCategory"]);
+  TextTheme get localTextGeometry => MaterialTextGeometry.forScriptCategory(_nameToValue['scriptCategory']);
 
   /// Creates an object that provides localized resource values for the
   /// for the widgets of the material library.

packages/flutter_test/lib/src/binding.dart

@@ -142,7 +142,7 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
     createHttpClient = () {
       return new http.MockClient((http.BaseRequest request) {
         return new Future<http.Response>.value(
-          new http.Response("Mocked: Unavailable.", 404, request: request)
+          new http.Response('Mocked: Unavailable.', 404, request: request)
         );
       });
     };

packages/flutter_test/test/matchers_test.dart

@@ -26,7 +26,7 @@ class _MockToStringDeep {
   /// line break.
   List<String> _lines;
 
-  String toStringDeep({ String prefixLineOne: "", String prefixOtherLines: "" }) {
+  String toStringDeep({ String prefixLineOne: '', String prefixOtherLines: '' }) {
     final StringBuffer sb = new StringBuffer();
     if (_lines.isNotEmpty)
       sb.write('$prefixLineOne${_lines.first}');

packages/flutter_tools/bin/fuchsia_tester.dart

@@ -26,9 +26,9 @@ import '../lib/src/usage.dart';
 
 // Note: this was largely inspired by lib/src/commands/test.dart.
 
-const String _kOptionPackages = "packages";
-const String _kOptionShell = "shell";
-const String _kOptionTestDirectory = "test-directory";
+const String _kOptionPackages = 'packages';
+const String _kOptionShell = 'shell';
+const String _kOptionTestDirectory = 'test-directory';
 const List<String> _kRequiredOptions = const <String>[
   _kOptionPackages,
   _kOptionShell,

packages/flutter_tools/lib/executable.dart

@@ -175,7 +175,7 @@ Future<int> _handleToolError(
     writelnStderr();
     writelnStderr(
         "Run 'flutter -h' (or 'flutter <command> -h') for available "
-            "flutter commands and options."
+            'flutter commands and options.'
     );
     // Argument error exit code.
     return _exit(64);

packages/flutter_tools/lib/src/android/android_device.dart

@@ -772,7 +772,7 @@ class _AndroidDevicePortForwarder extends DevicePortForwarder {
     final List<String> lines = LineSplitter.split(stdout).toList();
     for (String line in lines) {
       if (line.startsWith(device.id)) {
-        final List<String> splitLine = line.split("tcp:");
+        final List<String> splitLine = line.split('tcp:');
 
         // Sanity check splitLine.
         if (splitLine.length != 3)

packages/flutter_tools/lib/src/android/gradle.dart

@@ -43,7 +43,7 @@ FlutterPluginVersion get flutterPluginVersion {
   final File plugin = fs.file('android/buildSrc/src/main/groovy/FlutterPlugin.groovy');
   if (plugin.existsSync()) {
     final String packageLine = plugin.readAsLinesSync().skip(4).first;
-    if (packageLine == "package io.flutter.gradle") {
+    if (packageLine == 'package io.flutter.gradle') {
       return FlutterPluginVersion.v2;
     }
     return FlutterPluginVersion.v1;
@@ -51,7 +51,7 @@ FlutterPluginVersion get flutterPluginVersion {
   final File appGradle = fs.file('android/app/build.gradle');
   if (appGradle.existsSync()) {
     for (String line in appGradle.readAsLinesSync()) {
-      if (line.contains(new RegExp(r"apply from: .*/flutter.gradle"))) {
+      if (line.contains(new RegExp(r'apply from: .*/flutter.gradle'))) {
         return FlutterPluginVersion.managed;
       }
     }

packages/flutter_tools/lib/src/application_package.dart

@@ -116,7 +116,7 @@ class AndroidApk extends ApplicationPackage {
       if (category.getAttribute('android:name') == 'android.intent.category.LAUNCHER') {
         final xml.XmlElement activity = category.parent.parent;
         final String activityName = activity.getAttribute('android:name');
-        launchActivity = "$packageId/$activityName";
+        launchActivity = '$packageId/$activityName';
         break;
       }
     }

packages/flutter_tools/lib/src/base/common.dart

@@ -40,5 +40,5 @@ class ToolExit implements Exception {
   final int exitCode;
 
   @override
-  String toString() => "Exception: $message";
+  String toString() => 'Exception: $message';
 }

packages/flutter_tools/lib/src/base/os.dart

@@ -118,13 +118,13 @@ class _PosixUtils extends OperatingSystemUtils {
     if (_name == null) {
       if (platform.isMacOS) {
         final List<ProcessResult> results = <ProcessResult>[
-          processManager.runSync(<String>["sw_vers", "-productName"]),
-          processManager.runSync(<String>["sw_vers", "-productVersion"]),
-          processManager.runSync(<String>["sw_vers", "-buildVersion"]),
+          processManager.runSync(<String>['sw_vers', '-productName']),
+          processManager.runSync(<String>['sw_vers', '-productVersion']),
+          processManager.runSync(<String>['sw_vers', '-buildVersion']),
         ];
         if (results.every((ProcessResult result) => result.exitCode == 0)) {
-          _name = "${results[0].stdout.trim()} ${results[1].stdout
-              .trim()} ${results[2].stdout.trim()}";
+          _name = '${results[0].stdout.trim()} ${results[1].stdout
+              .trim()} ${results[2].stdout.trim()}';
         }
       }
       _name ??= super.name;

packages/flutter_tools/lib/src/base/process.dart

@@ -298,7 +298,7 @@ void _traceCommand(List<String> args, { String workingDirectory }) {
   if (workingDirectory == null)
     printTrace(argsText);
   else
-    printTrace("[$workingDirectory${fs.path.separator}] $argsText");
+    printTrace('[$workingDirectory${fs.path.separator}] $argsText');
 }
 
 String _runWithLoggingSync(List<String> cmd, {

packages/flutter_tools/lib/src/commands/build_aot.dart

@@ -239,10 +239,10 @@ Future<String> _buildAotSnapshot(
   ];
 
   if ((extraFrontEndOptions != null) && extraFrontEndOptions.isNotEmpty)
-    printTrace("Extra front-end options: $extraFrontEndOptions");
+    printTrace('Extra front-end options: $extraFrontEndOptions');
 
   if ((extraGenSnapshotOptions != null) && extraGenSnapshotOptions.isNotEmpty) {
-    printTrace("Extra gen-snapshot options: $extraGenSnapshotOptions");
+    printTrace('Extra gen-snapshot options: $extraGenSnapshotOptions');
     genSnapshotCmd.addAll(extraGenSnapshotOptions);
   }
 

packages/flutter_tools/lib/src/commands/create.dart

@@ -83,7 +83,7 @@ class CreateCommand extends FlutterCommand {
     'If run on a project that already exists, this will repair the project, recreating any files that are missing.';
 
   @override
-  String get invocation => "${runner.executableName} $name <output directory>";
+  String get invocation => '${runner.executableName} $name <output directory>';
 
   @override
   Future<Null> runCommand() async {
@@ -249,17 +249,17 @@ To edit platform code in an IDE see https://flutter.io/platform-plugins/#edit-co
       }
     } else {
       printStatus("You'll need to install additional components before you can run "
-        "your Flutter app:");
+        'your Flutter app:');
       printStatus('');
 
       // Give the user more detailed analysis.
       await doctor.diagnose();
       printStatus('');
       printStatus("After installing components, run 'flutter doctor' in order to "
-        "re-validate your setup.");
+        're-validate your setup.');
       printStatus("When complete, type 'flutter run' from the '$relativeAppPath' "
-        "directory in order to launch your app.");
-      printStatus("Your main program file is: $relativeAppPath/lib/main.dart");
+        'directory in order to launch your app.');
+      printStatus('Your main program file is: $relativeAppPath/lib/main.dart');
     }
   }
 
@@ -290,7 +290,7 @@ To edit platform code in an IDE see https://flutter.io/platform-plugins/#edit-co
       'dartSdk': '$flutterRoot/bin/cache/dart-sdk',
       'androidMinApiLevel': android.minApiLevel,
       'androidSdkVersion': android_sdk.minimumAndroidSdkVersion,
-      'androidFlutterJar': "$flutterRoot/bin/cache/artifacts/engine/android-arm/flutter.jar",
+      'androidFlutterJar': '$flutterRoot/bin/cache/artifacts/engine/android-arm/flutter.jar',
       'withDriverTest': renderDriverTest,
       'pluginClass': pluginClass,
       'pluginDartClass': pluginDartClass,
@@ -333,7 +333,7 @@ String _createPluginClassName(String name) {
 
 String _createUTIIdentifier(String organization, String name) {
   // Create a UTI (https://en.wikipedia.org/wiki/Uniform_Type_Identifier) from a base name
-  final RegExp disallowed = new RegExp(r"[^a-zA-Z0-9\-\.\u0080-\uffff]+");
+  final RegExp disallowed = new RegExp(r'[^a-zA-Z0-9\-\.\u0080-\uffff]+');
   name = camelCase(name).replaceAll(disallowed, '');
   name = name.isEmpty ? 'untitled' : name;
   return '$organization.$name';
@@ -367,7 +367,7 @@ String _validateProjectName(String projectName) {
 
   if (_packageDependencies.contains(projectName)) {
     return "Invalid project name: '$projectName' - this will conflict with Flutter "
-      "package dependencies.";
+      'package dependencies.';
   }
   return null;
 }
@@ -376,7 +376,7 @@ String _validateProjectName(String projectName) {
 /// if we should disallow the directory name.
 String _validateProjectDir(String dirPath, { String flutterRoot }) {
   if (fs.path.isWithin(flutterRoot, dirPath)) {
-    return "Cannot create a project within the Flutter SDK.\n"
+    return 'Cannot create a project within the Flutter SDK.\n'
       "Target directory '$dirPath' is within the Flutter SDK at '$flutterRoot'.";
   }
 

packages/flutter_tools/lib/src/commands/daemon.dart

@@ -197,28 +197,28 @@ abstract class Domain {
 
   String _getStringArg(Map<String, dynamic> args, String name, { bool required: false }) {
     if (required && !args.containsKey(name))
-      throw "$name is required";
+      throw '$name is required';
     final dynamic val = args[name];
     if (val != null && val is! String)
-      throw "$name is not a String";
+      throw '$name is not a String';
     return val;
   }
 
   bool _getBoolArg(Map<String, dynamic> args, String name, { bool required: false }) {
     if (required && !args.containsKey(name))
-      throw "$name is required";
+      throw '$name is required';
     final dynamic val = args[name];
     if (val != null && val is! bool)
-      throw "$name is not a bool";
+      throw '$name is not a bool';
     return val;
   }
 
   int _getIntArg(Map<String, dynamic> args, String name, { bool required: false }) {
     if (required && !args.containsKey(name))
-      throw "$name is required";
+      throw '$name is required';
     final dynamic val = args[name];
     if (val != null && val is! int)
-      throw "$name is not an int";
+      throw '$name is not an int';
     return val;
   }
 

packages/flutter_tools/lib/src/commands/devices.dart

@@ -23,7 +23,7 @@ class DevicesCommand extends FlutterCommand {
     if (!doctor.canListAnything) {
       throwToolExit(
         "Unable to locate a development device; please run 'flutter doctor' for "
-        "information about installing additional components.",
+        'information about installing additional components.',
         exitCode: 1);
     }
 

packages/flutter_tools/lib/src/commands/format.dart

@@ -21,7 +21,7 @@ class FormatCommand extends FlutterCommand {
   final String description = 'Format one or more dart files.';
 
   @override
-  String get invocation => "${runner.executableName} $name <one or more paths>";
+  String get invocation => '${runner.executableName} $name <one or more paths>';
 
   @override
   Future<Null> runCommand() async {

packages/flutter_tools/lib/src/commands/fuchsia_reload.dart

@@ -256,9 +256,9 @@ class FuchsiaReloadCommand extends FlutterCommand {
 
     // The Observatory requires somewhat non-standard URIs that the Uri class
     // can't build for us, so instead we build them by hand.
-    final String isolateIdQuery = "?isolateId=isolates%2F$number";
-    final String isolateAddr = "$vmServiceAddr/#/inspect$isolateIdQuery";
-    final String debuggerAddr = "$vmServiceAddr/#/debugger$isolateIdQuery";
+    final String isolateIdQuery = '?isolateId=isolates%2F$number';
+    final String isolateAddr = '$vmServiceAddr/#/inspect$isolateIdQuery';
+    final String debuggerAddr = '$vmServiceAddr/#/debugger$isolateIdQuery';
 
     final String newUsed = getSizeAsMB(isolate.newSpace.used);
     final String newCap = getSizeAsMB(isolate.newSpace.capacity);
@@ -452,7 +452,7 @@ class _PortForwarder {
     final ProcessResult result = await processManager.run(command);
     printTrace(command.join(' '));
     if (result.exitCode != 0) {
-      printTrace("Command failed:\nstdout: ${result.stdout}\nstderr: ${result.stderr}");
+      printTrace('Command failed:\nstdout: ${result.stdout}\nstderr: ${result.stderr}');
     }
   }
 
@@ -487,7 +487,7 @@ class FuchsiaDeviceCommandRunner {
     printTrace(args.join(' '));
     final ProcessResult result = await processManager.run(args);
     if (result.exitCode != 0) {
-      printStatus("Command failed: $command\nstdout: ${result.stdout}\nstderr: ${result.stderr}");
+      printStatus('Command failed: $command\nstdout: ${result.stdout}\nstderr: ${result.stderr}');
       return null;
     }
     printTrace(result.stdout);

packages/flutter_tools/lib/src/devfs.dart

@@ -498,10 +498,10 @@ class DevFS {
         try {
           await _httpWriter.write(dirtyEntries);
         } on SocketException catch (socketException, stackTrace) {
-          printTrace("DevFS sync failed. Lost connection to device: $socketException");
+          printTrace('DevFS sync failed. Lost connection to device: $socketException');
           throw new DevFSException('Lost connection to device.', socketException, stackTrace);
         } catch (exception, stackTrace) {
-          printError("Could not update files on device: $exception");
+          printError('Could not update files on device: $exception');
           throw new DevFSException('Sync failed', exception, stackTrace);
         }
       } else {

packages/flutter_tools/lib/src/device.dart

@@ -191,7 +191,7 @@ abstract class Device {
 
   // String meant to be displayed to the user indicating if the device is
   // supported by Flutter, and, if not, why.
-  String supportMessage() => isSupported() ? "Supported" : "Unsupported";
+  String supportMessage() => isSupported() ? 'Supported' : 'Unsupported';
 
   /// The device's platform.
   Future<TargetPlatform> get targetPlatform;

packages/flutter_tools/lib/src/ios/mac.dart

@@ -286,7 +286,7 @@ Future<XcodeBuildResult> buildXcodeProject({
       commands.addAll(<String>[
         '-workspace', fs.path.basename(entity.path),
         '-scheme', scheme,
-        "BUILD_DIR=${fs.path.absolute(getIosBuildDirectory())}",
+        'BUILD_DIR=${fs.path.absolute(getIosBuildDirectory())}',
       ]);
       break;
     }
@@ -447,20 +447,20 @@ bool _checkXcodeVersion() {
 
 Future<Null> _addServicesToBundle(Directory bundle) async {
   final List<Map<String, String>> services = <Map<String, String>>[];
-  printTrace("Trying to resolve native pub services.");
+  printTrace('Trying to resolve native pub services.');
 
   // Step 1: Parse the service configuration yaml files present in the service
   //         pub packages.
   await parseServiceConfigs(services);
-  printTrace("Found ${services.length} service definition(s).");
+  printTrace('Found ${services.length} service definition(s).');
 
   // Step 2: Copy framework dylibs to the correct spot for xcodebuild to pick up.
-  final Directory frameworksDirectory = fs.directory(fs.path.join(bundle.path, "Frameworks"));
+  final Directory frameworksDirectory = fs.directory(fs.path.join(bundle.path, 'Frameworks'));
   await _copyServiceFrameworks(services, frameworksDirectory);
 
   // Step 3: Copy the service definitions manifest at the correct spot for
   //         xcodebuild to pick up.
-  final File manifestFile = fs.file(fs.path.join(bundle.path, "ServiceDefinitions.json"));
+  final File manifestFile = fs.file(fs.path.join(bundle.path, 'ServiceDefinitions.json'));
   _copyServiceDefinitionsManifest(services, manifestFile);
 }
 
@@ -470,7 +470,7 @@ Future<Null> _copyServiceFrameworks(List<Map<String, String>> services, Director
   for (Map<String, String> service in services) {
     final String dylibPath = await getServiceFromUrl(service['ios-framework'], service['root'], service['name']);
     final File dylib = fs.file(dylibPath);
-    printTrace("Copying ${dylib.path} into bundle.");
+    printTrace('Copying ${dylib.path} into bundle.');
     if (!dylib.existsSync()) {
       printError("The service dylib '${dylib.path}' does not exist.");
       continue;

packages/flutter_tools/lib/src/ios/plist_utils.dart

@@ -5,8 +5,8 @@
 import '../base/file_system.dart';
 import '../base/process.dart';
 
-const String kCFBundleIdentifierKey = "CFBundleIdentifier";
-const String kCFBundleShortVersionStringKey = "CFBundleShortVersionString";
+const String kCFBundleIdentifierKey = 'CFBundleIdentifier';
+const String kCFBundleShortVersionStringKey = 'CFBundleShortVersionString';
 
 String getValueFromFile(String plistFilePath, String key) {
   // TODO(chinmaygarde): For now, we only need to read from plist files on a mac

packages/flutter_tools/lib/src/run_hot.dart

@@ -433,7 +433,7 @@ class HotRunner extends ResidentRunner {
         timer.stop();
         status.cancel();
         if (result.isOk)
-          printStatus("${result.message} in ${getElapsedAsMilliseconds(timer.elapsed)}.");
+          printStatus('${result.message} in ${getElapsedAsMilliseconds(timer.elapsed)}.');
         if (result.hint != null)
           printStatus(result.hint);
         return result;
@@ -530,7 +530,7 @@ class HotRunner extends ResidentRunner {
         reloadMessage = 'Reloaded $loadedLibraryCount of $finalLibraryCount libraries';
       }
     } catch (error, st) {
-      printError("Hot reload failed: $error\n$st");
+      printError('Hot reload failed: $error\n$st');
       final int errorCode = error['code'];
       final String errorMessage = error['message'];
       if (errorCode == Isolate.kIsolateReloadBarred) {
@@ -587,8 +587,8 @@ class HotRunner extends ResidentRunner {
         await view.uiIsolate.flutterReassemble();
       } on TimeoutException {
         reassembleTimedOut = true;
-        printTrace("Reassembling ${view.uiIsolate.name} took too long.");
-        printStatus("Hot reloading ${view.uiIsolate.name} took too long; the reload may have failed.");
+        printTrace('Reassembling ${view.uiIsolate.name} took too long.');
+        printStatus('Hot reloading ${view.uiIsolate.name} took too long; the reload may have failed.');
         continue;
       } catch (error) {
         reassembleAndScheduleErrors = true;

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -265,18 +265,18 @@ abstract class FlutterCommand extends Command<Null> {
   Future<List<Device>> findAllTargetDevices() async {
     if (!doctor.canLaunchAnything) {
       printError("Unable to locate a development device; please run 'flutter doctor' "
-          "for information about installing additional components.");
+          'for information about installing additional components.');
       return null;
     }
 
     List<Device> devices = await deviceManager.getDevices().toList();
 
     if (devices.isEmpty && deviceManager.hasSpecifiedDeviceId) {
-      printStatus("No devices found with name or id "
+      printStatus('No devices found with name or id '
           "matching '${deviceManager.specifiedDeviceId}'");
       return null;
     } else if (devices.isEmpty && deviceManager.hasSpecifiedAllDevices) {
-      printStatus("No devices found");
+      printStatus('No devices found');
       return null;
     } else if (devices.isEmpty) {
       printNoConnectedDevices();
@@ -290,10 +290,10 @@ abstract class FlutterCommand extends Command<Null> {
       return null;
     } else if (devices.length > 1 && !deviceManager.hasSpecifiedAllDevices) {
       if (deviceManager.hasSpecifiedDeviceId) {
-        printStatus("Found ${devices.length} devices with name or id matching "
+        printStatus('Found ${devices.length} devices with name or id matching '
             "'${deviceManager.specifiedDeviceId}':");
       } else {
-        printStatus("More than one device connected; please specify a device with "
+        printStatus('More than one device connected; please specify a device with '
             "the '-d <deviceId>' flag, or use '-d all' to act on all devices.");
         devices = await deviceManager.getAllConnectedDevices().toList();
       }
@@ -313,7 +313,7 @@ abstract class FlutterCommand extends Command<Null> {
     if (deviceList == null)
       return null;
     if (deviceList.length > 1) {
-      printStatus("More than one device connected; please specify a device with "
+      printStatus('More than one device connected; please specify a device with '
         "the '-d <deviceId>' flag.");
       deviceList = await deviceManager.getAllConnectedDevices().toList();
       printStatus('');

packages/flutter_tools/lib/src/services.dart

@@ -75,10 +75,10 @@ Future<Null> parseServiceConfigs(
 }
 
 Future<String> getServiceFromUrl(String url, String rootDir, String serviceName) async {
-  if (url.startsWith("android-sdk:") && androidSdk != null) {
+  if (url.startsWith('android-sdk:') && androidSdk != null) {
     // It's something shipped in the standard android SDK.
     return url.replaceAll('android-sdk:', '${androidSdk.directory}/');
-  } else if (url.startsWith("http")) {
+  } else if (url.startsWith('http')) {
     // It's a regular file to download.
     return await cache.getThirdPartyFile(url, serviceName);
   } else {

packages/flutter_tools/lib/src/template.dart

@@ -10,7 +10,7 @@ import 'globals.dart';
 
 const String _kTemplateExtension = '.tmpl';
 const String _kCopyTemplateExtension = '.copy.tmpl';
-final Pattern _kTemplateLanguageVariant = new RegExp(r"(\w+)-(\w+)\.tmpl.*");
+final Pattern _kTemplateLanguageVariant = new RegExp(r'(\w+)-(\w+)\.tmpl.*');
 
 /// Expands templates in a directory to a destination. All files that must
 /// undergo template expansion should end with the '.tmpl' extension. All other

packages/flutter_tools/lib/src/test/event_printer.dart

@@ -15,8 +15,8 @@ class EventPrinter extends TestWatcher {
 
   @override
   void onStartedProcess(ProcessEvent event) {
-    _sendEvent("test.startedProcess",
-        <String, dynamic>{"observatoryUri": event.observatoryUri.toString()});
+    _sendEvent('test.startedProcess',
+        <String, dynamic>{'observatoryUri': event.observatoryUri.toString()});
   }
 
   void _sendEvent(String name, [dynamic params]) {

packages/flutter_tools/lib/src/test/flutter_platform.dart

@@ -408,8 +408,8 @@ class _FlutterPlatform extends PlatformPlugin {
 
   String _getWebSocketUrl(HttpServer server) {
     return host.type == InternetAddressType.IP_V4
-        ? "ws://${host.address}:${server.port}"
-        : "ws://[${host.address}]:${server.port}";
+        ? 'ws://${host.address}:${server.port}'
+        : 'ws://[${host.address}]:${server.port}';
   }
 
   String _generateTestMain({

packages/flutter_tools/lib/src/test/runner.dart

@@ -44,11 +44,11 @@ Future<int> runTests(
   }
 
   for (String name in names) {
-    testArgs..add("--name")..add(name);
+    testArgs..add('--name')..add(name);
   }
 
   for (String plainName in plainNames) {
-    testArgs..add("--plain-name")..add(plainName);
+    testArgs..add('--plain-name')..add(plainName);
   }
 
   testArgs.add('--');

packages/flutter_tools/lib/src/vmservice.dart

@@ -321,7 +321,7 @@ abstract class ServiceObject {
       return null;
 
     if (!_isServiceMap(map))
-      throw new VMServiceObjectLoadError("Expected a service map", map);
+      throw new VMServiceObjectLoadError('Expected a service map', map);
 
     final String type = _stripRef(map['type']);
 
@@ -435,7 +435,7 @@ abstract class ServiceObject {
     final String mapType = _stripRef(map['type']);
 
     if ((_type != null) && (_type != mapType)) {
-      throw new VMServiceObjectLoadError("ServiceObject types must not change",
+      throw new VMServiceObjectLoadError('ServiceObject types must not change',
                                          map);
     }
     _type = mapType;
@@ -443,7 +443,7 @@ abstract class ServiceObject {
 
     _canCache = map['fixedId'] == true;
     if ((_id != null) && (_id != map['id']) && _canCache) {
-      throw new VMServiceObjectLoadError("ServiceObject id changed", map);
+      throw new VMServiceObjectLoadError('ServiceObject id changed', map);
     }
     _id = map['id'];
 
@@ -1061,7 +1061,7 @@ class Isolate extends ServiceObjectOwner {
       if (ownerType == 'Library' || ownerType == '@Library')
         break;
       final String ownerName = owner['name'];
-      name = "$ownerName.$name";
+      name = '$ownerName.$name';
       owner = owner['owner'];
     }
 

packages/flutter_tools/test/asset_bundle_package_fonts_test.dart

@@ -47,7 +47,7 @@ $fontsSection
   }
 
   void writePackagesFile(String packages) {
-    fs.file(".packages")
+    fs.file('.packages')
       ..createSync()
       ..writeAsStringSync(packages);
   }

packages/flutter_tools/test/asset_bundle_package_test.dart

@@ -55,7 +55,7 @@ $assetsSection
   }
 
   void writePackagesFile(String packages) {
-    fs.file(".packages")
+    fs.file('.packages')
       ..createSync()
       ..writeAsStringSync(packages);
   }
@@ -155,7 +155,7 @@ $assetsSection
         expectedAssetManifest,
       );
     }, overrides: contextOverrides);
-    
+
     testUsingContext("One asset is bundled when the package has one asset, listed in the app's pubspec", () async {
       establishFlutterRoot();
 
@@ -180,7 +180,7 @@ $assetsSection
       );
     }, overrides: contextOverrides);
 
-    testUsingContext("One asset and its variant are bundled when the package has an asset and a variant, and lists the asset in its pubspec", () async {
+    testUsingContext('One asset and its variant are bundled when the package has an asset and a variant, and lists the asset in its pubspec', () async {
       establishFlutterRoot();
 
       writePubspecFile('pubspec.yaml', 'test');
@@ -204,7 +204,7 @@ $assetsSection
       );
     }, overrides: contextOverrides);
 
-    testUsingContext("One asset and its variant are bundled when the package has an asset and a variant, and the app lists the asset in its pubspec", () async {
+    testUsingContext('One asset and its variant are bundled when the package has an asset and a variant, and the app lists the asset in its pubspec', () async {
       establishFlutterRoot();
 
       writePubspecFile(
@@ -231,7 +231,7 @@ $assetsSection
       );
     }, overrides: contextOverrides);
 
-    testUsingContext("Two assets are bundled when the package has and lists two assets in its pubspec", () async {
+    testUsingContext('Two assets are bundled when the package has and lists two assets in its pubspec', () async {
       establishFlutterRoot();
 
       writePubspecFile('pubspec.yaml', 'test');
@@ -288,7 +288,7 @@ $assetsSection
       );
     }, overrides: contextOverrides);
 
-    testUsingContext("Two assets are bundled when two packages each have and list an asset their pubspec", () async {
+    testUsingContext('Two assets are bundled when two packages each have and list an asset their pubspec', () async {
       establishFlutterRoot();
 
       writePubspecFile(
@@ -323,7 +323,7 @@ $assetsSection
         expectedAssetManifest,
       );
     }, overrides: contextOverrides);
-    
+
     testUsingContext("Two assets are bundled when two packages each have an asset, listed in the app's pubspec", () async {
       establishFlutterRoot();
 
@@ -363,7 +363,7 @@ $assetsSection
       );
     }, overrides: contextOverrides);
 
-    testUsingContext("One asset is bundled when the app depends on a package, listing in its pubspec an asset from another package", () async {
+    testUsingContext('One asset is bundled when the app depends on a package, listing in its pubspec an asset from another package', () async {
       establishFlutterRoot();
       writePubspecFile(
         'pubspec.yaml',

packages/flutter_tools/test/asset_bundle_variant_test.dart

@@ -23,7 +23,7 @@ void main()  {
       // path separator.
       Cache.flutterRoot = getFlutterRoot();
 
-      fs.file("pubspec.yaml")
+      fs.file('pubspec.yaml')
         ..createSync()
         ..writeAsStringSync(
 '''
@@ -36,7 +36,7 @@ flutter:
     - a/b/c/foo
 '''
       );
-      fs.file(".packages")..createSync();
+      fs.file('.packages')..createSync();
 
       final List<String> assets = <String>[
         'a/b/c/foo',

packages/flutter_tools/test/commands/create_test.dart

@@ -261,7 +261,7 @@ void main() {
       Cache.flutterRoot = '../..';
       final CreateCommand command = new CreateCommand();
       final CommandRunner<Null> runner = createTestCommandRunner(command);
-      final File existingFile = fs.file("${projectDir.path.toString()}/bad");
+      final File existingFile = fs.file('${projectDir.path.toString()}/bad');
       if (!existingFile.existsSync())
         existingFile.createSync(recursive: true);
       expect(

packages/flutter_tools/test/commands/packages_test.dart

@@ -277,12 +277,12 @@ class MemoryIOSink implements IOSink {
   }
 
   @override
-  void writeln([Object obj = ""]) {
+  void writeln([Object obj = '']) {
     add(encoding.encode('$obj\n'));
   }
 
   @override
-  void writeAll(Iterable<dynamic> objects, [String separator = ""]) {
+  void writeAll(Iterable<dynamic> objects, [String separator = '']) {
     bool addSeparator = false;
     for (dynamic object in objects) {
       if (addSeparator) {