Avoid 'as' keyword

It has performance implications in release mode.

We'll enable the lint once https://github.com/dart-lang/linter/issues/195 is fixed.

packages/flutter/test/rendering/stack_test.dart

@@ -27,7 +27,8 @@ void main() {
     );
 
     RenderBox stack = new RenderStack(children: <RenderBox>[red, green]);
-    (green.parentData as StackParentData)
+    StackParentData greenParentData = green.parentData;
+    greenParentData
       ..top = 0.0
       ..right = 0.0
       ..bottom = 0.0

packages/flutter/test/widget/asset_vendor_test.dart

@@ -69,7 +69,7 @@ class TestAssetBundle extends AssetBundle {
 }
 
 Future<ui.Image> testDecodeImageFromDataPipe(core.MojoDataPipeConsumer pipe) {
-  TestMojoDataPipeConsumer testPipe = pipe as TestMojoDataPipeConsumer;
+  TestMojoDataPipeConsumer testPipe = pipe;
   assert(testPipe != null);
   ui.Image image = new TestImage(testPipe.scale);
   return (new Completer<ui.Image>()..complete(image)).future;
@@ -108,11 +108,11 @@ Widget buildImageAtRatio(String image, Key key, double ratio, bool inferSize) {
 }
 
 RenderImage getRenderImage(tester, Key key) {
-  return tester.findElementByKey(key).renderObject as RenderImage;
+  return tester.findElementByKey(key).renderObject;
 }
 
 TestImage getTestImage(tester, Key key) {
-  return getRenderImage(tester, key).image as TestImage;
+  return getRenderImage(tester, key).image;
 }
 
 void pumpTreeToLayout(WidgetTester tester, Widget widget) {

packages/flutter/test/widget/build_scope_test.dart

@@ -104,10 +104,12 @@ void main() {
         right: new ProbeWidget()
       ));
       expect(ProbeWidgetState.buildCount, equals(2));
-      (flipKey.currentState as FlipComponentState).flip();
+      FlipComponentState flipState1 = flipKey.currentState;
+      flipState1.flip();
       tester.pump();
       expect(ProbeWidgetState.buildCount, equals(3));
-      (flipKey.currentState as FlipComponentState).flip();
+      FlipComponentState flipState2 = flipKey.currentState;
+      flipState2.flip();
       tester.pump();
       expect(ProbeWidgetState.buildCount, equals(3));
       tester.pumpWidget(new Container());

packages/flutter/test/widget/coordinates_test.dart

@@ -38,14 +38,12 @@ void main() {
         )
       );
 
-      expect((tester.findElementByKey(keyA).renderObject as RenderBox).localToGlobal(const Point(0.0, 0.0)),
-             equals(const Point(100.0, 100.0)));
+      RenderBox boxA = tester.findElementByKey(keyA).renderObject;
+      expect(boxA.localToGlobal(const Point(0.0, 0.0)), equals(const Point(100.0, 100.0)));
 
-      expect((tester.findElementByKey(keyB).renderObject as RenderBox).localToGlobal(const Point(0.0, 0.0)),
-             equals(const Point(100.0, 200.0)));
-
-      expect((tester.findElementByKey(keyB).renderObject as RenderBox).globalToLocal(const Point(110.0, 205.0)),
-             equals(const Point(10.0, 5.0)));
+      RenderBox boxB = tester.findElementByKey(keyB).renderObject;
+      expect(boxB.localToGlobal(const Point(0.0, 0.0)), equals(const Point(100.0, 200.0)));
+      expect(boxB.globalToLocal(const Point(110.0, 205.0)), equals(const Point(10.0, 5.0)));
     });
   });
 }

packages/flutter/test/widget/input_test.dart

@@ -48,7 +48,8 @@ void main() {
       tester.pumpWidget(builder());
 
       Element input = tester.findElementByKey(inputKey);
-      Size emptyInputSize = (input.renderObject as RenderBox).size;
+      RenderBox inputBox = input.renderObject;
+      Size emptyInputSize = inputBox.size;
 
       void enterText(String testValue) {
         // Simulate entry of text through the keyboard.
@@ -65,10 +66,12 @@ void main() {
       }
 
       enterText(' ');
-      expect((input.renderObject as RenderBox).size, equals(emptyInputSize));
+      expect(input.renderObject, equals(inputBox));
+      expect(inputBox.size, equals(emptyInputSize));
 
       enterText('Test');
-      expect((input.renderObject as RenderBox).size, equals(emptyInputSize));
+      expect(input.renderObject, equals(inputBox));
+      expect(inputBox.size, equals(emptyInputSize));
     });
   });
 

packages/flutter/test/widget/parent_data_test.dart

@@ -35,7 +35,8 @@ void checkTree(WidgetTester tester, List<TestParentData> expectedParentData) {
       expect(parentData.right, equals(expected.right));
       expect(parentData.bottom, equals(expected.bottom));
       expect(parentData.left, equals(expected.left));
-      child = (decoratedBox.parentData as StackParentData).nextSibling;
+      StackParentData decoratedBoxParentData = decoratedBox.parentData;
+      child = decoratedBoxParentData.nextSibling;
     }
     expect(child, isNull);
   } catch (e) {

packages/flutter/test/widget/reparent_state_test.dart

@@ -47,8 +47,10 @@ void main() {
         )
       );
 
-      (left.currentState as StateMarkerState).marker = "left";
-      (right.currentState as StateMarkerState).marker = "right";
+      StateMarkerState leftState = left.currentState;
+      leftState.marker = "left";
+      StateMarkerState rightState = right.currentState;
+      rightState.marker = "right";
 
       StateMarkerState grandchildState = tester.findStateByConfig(grandchild);
       expect(grandchildState, isNotNull);
@@ -71,8 +73,10 @@ void main() {
         )
       );
 
-      expect((left.currentState as StateMarkerState).marker, equals("left"));
-      expect((right.currentState as StateMarkerState).marker, equals("right"));
+      expect(left.currentState, equals(leftState));
+      expect(leftState.marker, equals("left"));
+      expect(right.currentState, equals(rightState));
+      expect(rightState.marker, equals("right"));
 
       StateMarkerState newGrandchildState = tester.findStateByConfig(newGrandchild);
       expect(newGrandchildState, isNotNull);
@@ -90,7 +94,8 @@ void main() {
         )
       );
 
-      expect((left.currentState as StateMarkerState).marker, equals("left"));
+      expect(left.currentState, equals(leftState));
+      expect(leftState.marker, equals("left"));
       expect(right.currentState, isNull);
     });
   });
@@ -113,8 +118,10 @@ void main() {
         )
       );
 
-      (left.currentState as StateMarkerState).marker = "left";
-      (right.currentState as StateMarkerState).marker = "right";
+      StateMarkerState leftState = left.currentState;
+      leftState.marker = "left";
+      StateMarkerState rightState = right.currentState;
+      rightState.marker = "right";
 
       StateMarkerState grandchildState = tester.findStateByConfig(grandchild);
       expect(grandchildState, isNotNull);
@@ -133,8 +140,10 @@ void main() {
         )
       );
 
-      expect((left.currentState as StateMarkerState).marker, equals("left"));
-      expect((right.currentState as StateMarkerState).marker, equals("right"));
+      expect(left.currentState, equals(leftState));
+      expect(leftState.marker, equals("left"));
+      expect(right.currentState, equals(rightState));
+      expect(rightState.marker, equals("right"));
 
       StateMarkerState newGrandchildState = tester.findStateByConfig(newGrandchild);
       expect(newGrandchildState, isNotNull);
@@ -152,7 +161,8 @@ void main() {
         )
       );
 
-      expect((left.currentState as StateMarkerState).marker, equals("left"));
+      expect(left.currentState, equals(leftState));
+      expect(leftState.marker, equals("left"));
       expect(right.currentState, isNull);
     });
   });
@@ -163,7 +173,8 @@ void main() {
 
       tester.pumpWidget(new StateMarker(key: key));
 
-      (key.currentState as StateMarkerState).marker = "marked";
+      StateMarkerState keyState = key.currentState;
+      keyState.marker = "marked";
 
       tester.pumpWidget(new ScrollableList(
         itemExtent: 100.0,
@@ -176,11 +187,13 @@ void main() {
         ]
       ));
 
-      expect((key.currentState as StateMarkerState).marker, equals("marked"));
+      expect(key.currentState, equals(keyState));
+      expect(keyState.marker, equals("marked"));
 
       tester.pumpWidget(new StateMarker(key: key));
 
-      expect((key.currentState as StateMarkerState).marker, equals("marked"));
+      expect(key.currentState, equals(keyState));
+      expect(keyState.marker, equals("marked"));
     });
   });
 }

packages/flutter_test/lib/src/instrumentation.dart

@@ -138,14 +138,14 @@ class Instrumentation {
   /// the element's render object has been laid out at least once.
   Size getSize(Element element) {
     assert(element != null);
-    RenderBox box = element.renderObject as RenderBox;
+    RenderBox box = element.renderObject;
     assert(box != null);
     return box.size;
   }
 
   Point _getElementPoint(Element element, SizeToPointFunction sizeToPoint) {
     assert(element != null);
-    RenderBox box = element.renderObject as RenderBox;
+    RenderBox box = element.renderObject;
     assert(box != null);
     return box.localToGlobal(sizeToPoint(box.size));
   }

packages/flutter_tools/lib/src/application_package.dart

@@ -68,7 +68,7 @@ class AndroidApk extends ApplicationPackage {
     String launchActivity;
     for (xml.XmlElement category in document.findAllElements('category')) {
       if (category.getAttribute('android:name') == 'android.intent.category.LAUNCHER') {
-        xml.XmlElement activity = category.parent.parent as xml.XmlElement;
+        xml.XmlElement activity = category.parent.parent;
         String activityName = activity.getAttribute('android:name');
         launchActivity = "$id/$activityName";
         break;

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

@@ -294,9 +294,10 @@ class AnalyzeCommand extends FlutterCommand {
     for (String package in packages.keys)
       packagesBody.writeln('$package:${path.toUri(packages[package])}');
 
-    /// specify analysis options
-    /// note that until there is a default "all-in" lint rule-set we need
-    /// to opt-in to all desired lints (https://github.com/dart-lang/sdk/issues/25843)
+    /// Specify analysis options.
+    /// Note that until there is a default "all-in" lint rule-set we need
+    /// to opt-in to all desired lints (https://github.com/dart-lang/sdk/issues/25843).
+    /// For a list of lints, see: http://dart-lang.github.io/linter/lints/
     String optionsBody = '''
 analyzer:
   errors:
@@ -307,6 +308,8 @@ analyzer:
     todo: ignore
 linter:
   rules:
+    # we'll turn on avoid_as as soon as it doesn't complain about "as dynamic"
+    # - avoid_as
     - camel_case_types
     # sometimes we have no choice (e.g. when matching other platforms)
     # - constant_identifier_names