Add API for specifying the system overlay style. (#4422)

Fixes 3544

dev/manual_tests/overlay_geometry.dart

@@ -196,7 +196,7 @@ class OverlayGeometryAppState extends State<OverlayGeometryApp> {
 void main() {
   runApp(new MaterialApp(
     theme: new ThemeData(
-      brightness: ThemeBrightness.light,
+      brightness: Brightness.light,
       primarySwatch: Colors.blue,
       accentColor: Colors.redAccent[200]
     ),

dev/manual_tests/pageable_list.dart

@@ -145,7 +145,7 @@ void main() {
   runApp(new MaterialApp(
     title: 'PageableList',
     theme: new ThemeData(
-      brightness: ThemeBrightness.light,
+      brightness: Brightness.light,
       primarySwatch: Colors.blue,
       accentColor: Colors.redAccent[200]
     ),

examples/flutter_gallery/lib/demo/calculator_demo.dart

@@ -160,7 +160,7 @@ class KeyPad extends StatelessWidget {
     return new Theme(
       data: new ThemeData(
         primarySwatch: Colors.purple,
-        brightness: ThemeBrightness.dark
+        brightness: Brightness.dark
       ),
       child: new Flexible(
         flex: _flex,

examples/flutter_gallery/lib/demo/contacts_demo.dart

@@ -87,7 +87,7 @@ class ContactsDemoState extends State<ContactsDemo> {
     final double statusBarHeight = MediaQuery.of(context).padding.top;
     return new Theme(
       data: new ThemeData(
-        brightness: ThemeBrightness.light,
+        brightness: Brightness.light,
         primarySwatch: Colors.indigo
       ),
       child: new Scaffold(

examples/flutter_gallery/lib/demo/pesto_demo.dart

@@ -14,7 +14,7 @@ final Map<double, String> _kLogoImages = <double, String>{
   170.0: 'packages/flutter_gallery_assets/pesto/logo_big.png',
 };
 final ThemeData _kTheme = new ThemeData(
-  brightness: ThemeBrightness.light,
+  brightness: Brightness.light,
   primarySwatch: Colors.teal,
   accentColor: Colors.redAccent[200]
 );

examples/flutter_gallery/lib/gallery/app.dart

@@ -45,12 +45,12 @@ final Map<String, WidgetBuilder> kRoutes = <String, WidgetBuilder>{
 };
 
 final ThemeData _kGalleryLightTheme = new ThemeData(
-  brightness: ThemeBrightness.light,
+  brightness: Brightness.light,
   primarySwatch: Colors.purple
 );
 
 final ThemeData _kGalleryDarkTheme = new ThemeData(
-  brightness: ThemeBrightness.dark,
+  brightness: Brightness.dark,
   primarySwatch: Colors.purple
 );
 

examples/stocks/lib/main.dart

@@ -66,12 +66,12 @@ class StocksAppState extends State<StocksApp> {
     switch (_configuration.stockMode) {
       case StockMode.optimistic:
         return new ThemeData(
-          brightness: ThemeBrightness.light,
+          brightness: Brightness.light,
           primarySwatch: Colors.purple
         );
       case StockMode.pessimistic:
         return new ThemeData(
-          brightness: ThemeBrightness.dark,
+          brightness: Brightness.dark,
           accentColor: Colors.redAccent[200]
         );
     }

packages/flutter/lib/src/material/app.dart

@@ -177,6 +177,7 @@ class _MaterialAppState extends State<MaterialApp> {
       child: new WidgetsApp(
         title: config.title,
         textStyle: _errorTextStyle,
+        brightness: theme.brightness,
         color: theme?.primaryColor ?? Colors.blue[500], // blue[500] is the primary color of the default theme
         navigatorObserver: _heroController,
         onGenerateRoute: _onGenerateRoute,

packages/flutter/lib/src/material/button.dart

@@ -129,7 +129,7 @@ class MaterialButton extends StatefulWidget {
   /// The theme brightness to use for this button.
   ///
   /// Defaults to the brightness from [ThemeData.brightness].
-  final ThemeBrightness colorBrightness;
+  final Brightness colorBrightness;
 
   /// The color scheme to use for this button's text.
   ///
@@ -193,7 +193,7 @@ class MaterialButton extends StatefulWidget {
 class _MaterialButtonState extends State<MaterialButton> {
   bool _highlight = false;
 
-  ThemeBrightness get _colorBrightness {
+  Brightness get _colorBrightness {
     return config.colorBrightness ?? Theme.of(context).brightness;
   }
 
@@ -206,17 +206,17 @@ class _MaterialButtonState extends State<MaterialButton> {
           return Theme.of(context).accentColor;
         case ButtonTextTheme.normal:
           switch (_colorBrightness) {
-            case ThemeBrightness.light:
+            case Brightness.light:
               return Colors.black87;
-            case ThemeBrightness.dark:
+            case Brightness.dark:
               return Colors.white;
           }
       }
     } else {
       switch (_colorBrightness) {
-        case ThemeBrightness.light:
+        case Brightness.light:
           return Colors.black26;
-        case ThemeBrightness.dark:
+        case Brightness.dark:
           return Colors.white30;
       }
     }

packages/flutter/lib/src/material/date_picker.dart

@@ -158,11 +158,11 @@ class _DatePickerHeader extends StatelessWidget {
     Color dayColor;
     Color yearColor;
     switch(themeData.primaryColorBrightness) {
-      case ThemeBrightness.light:
+      case Brightness.light:
         dayColor = mode == _DatePickerMode.day ? Colors.black87 : Colors.black54;
         yearColor = mode == _DatePickerMode.year ? Colors.black87 : Colors.black54;
         break;
-      case ThemeBrightness.dark:
+      case Brightness.dark:
         dayColor = mode == _DatePickerMode.day ? Colors.white : Colors.white70;
         yearColor = mode == _DatePickerMode.year ? Colors.white : Colors.white70;
         break;
@@ -172,10 +172,10 @@ class _DatePickerHeader extends StatelessWidget {
 
     Color backgroundColor;
     switch (themeData.brightness) {
-      case ThemeBrightness.light:
+      case Brightness.light:
         backgroundColor = themeData.primaryColor;
         break;
-      case ThemeBrightness.dark:
+      case Brightness.dark:
         backgroundColor = themeData.backgroundColor;
         break;
     }
@@ -299,7 +299,7 @@ class DayPicker extends StatelessWidget {
         if (selectedDate.year == year && selectedDate.month == month && selectedDate.day == day) {
           // The selected day gets a circle background highlight, and a contrasting text color.
           itemStyle = themeData.textTheme.body2.copyWith(
-            color: (themeData.brightness == ThemeBrightness.light) ? Colors.white : Colors.black87
+            color: (themeData.brightness == Brightness.light) ? Colors.white : Colors.black87
           );
           decoration = new BoxDecoration(
             backgroundColor: themeData.accentColor,

packages/flutter/lib/src/material/dialog.dart

@@ -58,9 +58,9 @@ class Dialog extends StatelessWidget {
 
   Color _getColor(BuildContext context) {
     switch (Theme.of(context).brightness) {
-      case ThemeBrightness.light:
+      case Brightness.light:
         return Colors.white;
-      case ThemeBrightness.dark:
+      case Brightness.dark:
         return Colors.grey[800];
     }
   }

packages/flutter/lib/src/material/drawer_item.dart

@@ -54,13 +54,13 @@ class DrawerItem extends StatelessWidget {
 
   Color _getIconColor(ThemeData themeData) {
     switch (themeData.brightness) {
-      case ThemeBrightness.light:
+      case Brightness.light:
         if (selected)
           return themeData.primaryColor;
         if (onPressed == null)
           return Colors.black26;
         return Colors.black45;
-      case ThemeBrightness.dark:
+      case Brightness.dark:
         if (selected)
           return themeData.accentColor;
         if (onPressed == null)
@@ -73,9 +73,9 @@ class DrawerItem extends StatelessWidget {
     TextStyle result = themeData.textTheme.body2;
     if (selected) {
       switch (themeData.brightness) {
-        case ThemeBrightness.light:
+        case Brightness.light:
           return result.copyWith(color: themeData.primaryColor);
-        case ThemeBrightness.dark:
+        case Brightness.dark:
           return result.copyWith(color: themeData.accentColor);
       }
     }

packages/flutter/lib/src/material/flat_button.dart

@@ -84,7 +84,7 @@ class FlatButton extends StatelessWidget {
   /// The theme brightness to use for this button.
   ///
   /// Defaults to the brightness from [ThemeData.brightness].
-  final ThemeBrightness colorBrightness;
+  final Brightness colorBrightness;
 
   /// The widget below this widget in the tree.
   ///

packages/flutter/lib/src/material/floating_action_button.dart

@@ -107,7 +107,7 @@ class _FloatingActionButtonState extends State<FloatingActionButton> {
     if (materialColor == null) {
       ThemeData themeData = Theme.of(context);
       materialColor = themeData.accentColor;
-      iconColor = themeData.accentColorBrightness == ThemeBrightness.dark ? Colors.white : Colors.black;
+      iconColor = themeData.accentColorBrightness == Brightness.dark ? Colors.white : Colors.black;
     }
 
     Widget result = new Center(

packages/flutter/lib/src/material/icon.dart

@@ -58,17 +58,17 @@ class Icon extends StatelessWidget {
   /// brightness.
   final Color color;
 
-  Color _getDefaultColorForThemeBrightness(ThemeBrightness brightness) {
+  Color _getDefaultColorForBrightness(Brightness brightness) {
     switch (brightness) {
-      case ThemeBrightness.dark:
+      case Brightness.dark:
         return Colors.white;
-      case ThemeBrightness.light:
+      case Brightness.light:
         return Colors.black;
     }
   }
 
   Color _getDefaultColor(BuildContext context) {
-    return IconTheme.of(context)?.color ?? _getDefaultColorForThemeBrightness(Theme.of(context).brightness);
+    return IconTheme.of(context)?.color ?? _getDefaultColorForBrightness(Theme.of(context).brightness);
   }
 
   @override

packages/flutter/lib/src/material/input.dart

@@ -117,10 +117,10 @@ class _InputState extends State<Input> {
     Color activeColor = themeData.hintColor;
     if (focused) {
       switch (themeData.brightness) {
-        case ThemeBrightness.dark:
+        case Brightness.dark:
           activeColor = themeData.accentColor;
           break;
-        case ThemeBrightness.light:
+        case Brightness.light:
           activeColor = themeData.primaryColor;
           break;
       }

packages/flutter/lib/src/material/popup_menu.dart

@@ -159,7 +159,7 @@ class _PopupMenuItemState<T extends PopupMenuItem<dynamic>> extends State<T> {
       )
     );
     if (!config.enabled) {
-      final bool isDark = theme.brightness == ThemeBrightness.dark;
+      final bool isDark = theme.brightness == Brightness.dark;
       item = new IconTheme(
         data: new IconThemeData(opacity: isDark ? 0.5 : 0.38),
         child: item

packages/flutter/lib/src/material/raised_button.dart

@@ -80,7 +80,7 @@ class RaisedButton extends StatelessWidget {
   /// The theme brightness to use for this button.
   ///
   /// Defaults to the brightness from [ThemeData.brightness].
-  final ThemeBrightness colorBrightness;
+  final Brightness colorBrightness;
 
   /// The widget below this widget in the tree.
   ///
@@ -98,9 +98,9 @@ class RaisedButton extends StatelessWidget {
       if (disabledColor != null)
         return disabledColor;
       switch (Theme.of(context).brightness) {
-        case ThemeBrightness.light:
+        case Brightness.light:
           return Colors.black12;
-        case ThemeBrightness.dark:
+        case Brightness.dark:
           return Colors.white12;
       }
     }

packages/flutter/lib/src/material/snack_bar.dart

@@ -175,7 +175,7 @@ class SnackBar extends StatelessWidget {
                 margin: const EdgeInsets.symmetric(horizontal: _kSideMargins),
                 child: new Theme(
                   data: new ThemeData(
-                    brightness: ThemeBrightness.dark,
+                    brightness: Brightness.dark,
                     accentColor: theme.accentColor,
                     accentColorBrightness: theme.accentColorBrightness,
                     textTheme: Typography.white

packages/flutter/lib/src/material/switch.dart

@@ -80,7 +80,7 @@ class Switch extends StatelessWidget {
   Widget build(BuildContext context) {
     assert(debugCheckHasMaterial(context));
     ThemeData themeData = Theme.of(context);
-    final bool isDark = themeData.brightness == ThemeBrightness.dark;
+    final bool isDark = themeData.brightness == Brightness.dark;
 
     Color activeThumbColor = activeColor ?? themeData.accentColor;
     Color activeTrackColor = activeThumbColor.withAlpha(0x80);

packages/flutter/lib/src/material/theme.dart

@@ -7,7 +7,7 @@ import 'package:meta/meta.dart';
 
 import 'theme_data.dart';
 
-export 'theme_data.dart' show ThemeData, ThemeBrightness;
+export 'theme_data.dart' show ThemeData;
 
 /// The duration over which theme changes animate.
 const Duration kThemeAnimationDuration = const Duration(milliseconds: 200);

packages/flutter/lib/src/material/theme_data.dart

@@ -4,28 +4,12 @@
 
 import 'dart:ui' show Color, hashValues;
 
+import 'package:flutter/widgets.dart';
+
 import 'colors.dart';
 import 'icon_theme_data.dart';
 import 'typography.dart';
 
-/// The contrast needs of a color.
-///
-/// This is used to describe the contrast needs of a theme as a whole
-/// ([ThemeData.brightness]), its primary color
-/// ([ThemeData.primaryColorBrightness]), and its accent color
-/// ([ThemeData.accentColorBrightness]).
-enum ThemeBrightness {
-  /// The color is dark, and will require a light text color to achieve readable contrast.
-  ///
-  /// For example, the color might be dark grey, requiring white text.
-  dark,
-
-  /// The color is right, and will require a dark text color to achieve readable contrast.
-  ///
-  /// For example, the color might be bright white, requiring black text.
-  light,
-}
-
 // Deriving these values is black magic. The spec claims that pressed buttons
 // have a highlight of 0x66999999, but that's clearly wrong. The videos in the
 // spec show that buttons have a composited highlight of #E1E1E1 on a background
@@ -68,12 +52,12 @@ class ThemeData {
   /// See <https://www.google.com/design/spec/style/color.html> for
   /// more discussion on how to pick the right colors.
   factory ThemeData({
-    ThemeBrightness brightness,
+    Brightness brightness,
     Map<int, Color> primarySwatch,
     Color primaryColor,
-    ThemeBrightness primaryColorBrightness,
+    Brightness primaryColorBrightness,
     Color accentColor,
-    ThemeBrightness accentColorBrightness,
+    Brightness accentColorBrightness,
     Color canvasColor,
     Color cardColor,
     Color dividerColor,
@@ -93,13 +77,13 @@ class ThemeData {
     TextTheme primaryTextTheme,
     IconThemeData primaryIconTheme
   }) {
-    brightness ??= ThemeBrightness.light;
-    final bool isDark = brightness == ThemeBrightness.dark;
+    brightness ??= Brightness.light;
+    final bool isDark = brightness == Brightness.dark;
     primarySwatch ??= Colors.blue;
     primaryColor ??= isDark ? Colors.grey[900] : primarySwatch[500];
-    primaryColorBrightness ??= ThemeBrightness.dark;
+    primaryColorBrightness ??= Brightness.dark;
     accentColor ??= isDark ? Colors.tealAccent[200] : primarySwatch[500];
-    accentColorBrightness ??= ThemeBrightness.dark;
+    accentColorBrightness ??= Brightness.dark;
     canvasColor ??= isDark ? Colors.grey[850] : Colors.grey[50];
     cardColor ??= isDark ? Colors.grey[800] : Colors.white;
     dividerColor ??= isDark ? const Color(0x1FFFFFFF) : const Color(0x1F000000);
@@ -116,8 +100,8 @@ class ThemeData {
     hintColor ??= isDark ? const Color(0x42FFFFFF) : const Color(0x4C000000);
     errorColor ??= Colors.red[700];
     textTheme ??= isDark ? Typography.white : Typography.black;
-    primaryTextTheme ??= primaryColorBrightness == ThemeBrightness.dark ? Typography.white : Typography.black;
-    primaryIconTheme ??= primaryColorBrightness == ThemeBrightness.dark ? const IconThemeData(color: Colors.white) : const IconThemeData(color: Colors.black);
+    primaryTextTheme ??= primaryColorBrightness == Brightness.dark ? Typography.white : Typography.black;
+    primaryIconTheme ??= primaryColorBrightness == Brightness.dark ? const IconThemeData(color: Colors.white) : const IconThemeData(color: Colors.black);
     return new ThemeData.raw(
       brightness: brightness,
       primaryColor: primaryColor,
@@ -202,10 +186,10 @@ class ThemeData {
   }
 
   /// A default light blue theme.
-  factory ThemeData.light() => new ThemeData(brightness: ThemeBrightness.light);
+  factory ThemeData.light() => new ThemeData(brightness: Brightness.light);
 
   /// A default dark theme with a teal accent color.
-  factory ThemeData.dark() => new ThemeData(brightness: ThemeBrightness.dark);
+  factory ThemeData.dark() => new ThemeData(brightness: Brightness.dark);
 
   /// The default theme. Same as [new ThemeData.light].
   ///
@@ -216,20 +200,20 @@ class ThemeData {
   /// like buttons to determine what color to pick when not using the primary or
   /// accent color.
   ///
-  /// When the ThemeBrightness is dark, the canvas, card, and primary colors are
-  /// all dark. When the ThemeBrightness is light, the canvas and card colors
+  /// When the [Brightness] is dark, the canvas, card, and primary colors are
+  /// all dark. When the [Brightness] is light, the canvas and card colors
   /// are bright, and the primary color's darkness varies as described by
   /// primaryColorBrightness. The primaryColor does not contrast well with the
   /// card and canvas colors when the brightness is dark; when the brightness is
   /// dark, use Colors.white or the accentColor for a contrasting color.
-  final ThemeBrightness brightness;
+  final Brightness brightness;
 
   /// The background color for major parts of the app (toolbars, tab bars, etc)
   final Color primaryColor;
 
   /// The brightness of the primaryColor. Used to determine the color of text and
   /// icons placed on top of the primary color (e.g. toolbar text).
-  final ThemeBrightness primaryColorBrightness;
+  final Brightness primaryColorBrightness;
 
   /// The foreground color for widgets (knobs, text, etc)
   final Color accentColor;
@@ -237,7 +221,7 @@ class ThemeData {
   /// The brightness of the accentColor. Used to determine the color of text
   /// and icons placed on top of the accent color (e.g. the icons on a floating
   /// action button).
-  final ThemeBrightness accentColorBrightness;
+  final Brightness accentColorBrightness;
 
   /// The color of [Material] when it is of infinite extent, e.g. the
   /// body of a [Scaffold].

packages/flutter/lib/src/material/time_picker.dart

@@ -211,11 +211,11 @@ class _TimePickerHeader extends StatelessWidget {
     Color activeColor;
     Color inactiveColor;
     switch(themeData.primaryColorBrightness) {
-      case ThemeBrightness.light:
+      case Brightness.light:
         activeColor = Colors.black87;
         inactiveColor = Colors.black54;
         break;
-      case ThemeBrightness.dark:
+      case Brightness.dark:
         activeColor = Colors.white;
         inactiveColor = Colors.white70;
         break;
@@ -223,10 +223,10 @@ class _TimePickerHeader extends StatelessWidget {
 
     Color backgroundColor;
     switch (themeData.brightness) {
-      case ThemeBrightness.light:
+      case Brightness.light:
         backgroundColor = themeData.primaryColor;
         break;
-      case ThemeBrightness.dark:
+      case Brightness.dark:
         backgroundColor = themeData.backgroundColor;
         break;
     }
@@ -525,10 +525,10 @@ class _DialState extends State<_Dial> {
 
     Color backgroundColor;
     switch (themeData.brightness) {
-      case ThemeBrightness.light:
+      case Brightness.light:
         backgroundColor = Colors.grey[200];
         break;
-      case ThemeBrightness.dark:
+      case Brightness.dark:
         backgroundColor = themeData.backgroundColor;
         break;
     }
@@ -538,11 +538,11 @@ class _DialState extends State<_Dial> {
     switch (config.mode) {
       case _TimePickerMode.hour:
         switch (themeData.brightness) {
-          case ThemeBrightness.light:
+          case Brightness.light:
             primaryLabels = _hoursBlack;
             secondaryLabels = _hoursWhite;
             break;
-          case ThemeBrightness.dark:
+          case Brightness.dark:
             primaryLabels = _hoursWhite;
             secondaryLabels = _hoursBlack;
             break;
@@ -550,11 +550,11 @@ class _DialState extends State<_Dial> {
         break;
       case _TimePickerMode.minute:
         switch (themeData.brightness) {
-          case ThemeBrightness.light:
+          case Brightness.light:
             primaryLabels = _minutesBlack;
             secondaryLabels = _minutesWhite;
             break;
-          case ThemeBrightness.dark:
+          case Brightness.dark:
             primaryLabels = _minutesWhite;
             secondaryLabels = _minutesBlack;
             break;

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

@@ -37,14 +37,35 @@ class SystemChrome {
     return (await _systemChromeProxy.setPreferredOrientations(deviceOrientationMask)).success;
   }
 
+  /// Specifies the description of the current state of the application as it
+  /// pertains to the application switcher (a.k.a "recent tasks").
+  ///
+  /// Arguments:
+  ///
+  ///  * [description]: The application description.
+  ///
+  /// Return Value:
+  ///
+  ///   boolean indicating if the description was conveyed successfully to the
+  ///   embedder.
+  ///
+  /// Platform Specific Notes:
+  ///
+  ///   If application-specified metadata is unsupported on the platform,
+  ///   specifying it is a no-op and always return true.
+  static Future<bool> setApplicationSwitcherDescription(mojom.ApplicationSwitcherDescription description) async {
+    return (await _systemChromeProxy.setApplicationSwitcherDescription(
+      description)).success;
+  }
+
   /// Specifies the set of overlays visible on the embedder when the
   /// application is running. The embedder may choose to ignore unsupported
   /// overlays
   ///
   /// Arguments:
   ///
-  ///  * [style]: A mask of [SystemUIOverlay] enum values that denotes the overlays
-  ///    to show.
+  ///  * [overlaysMask]: A mask of [SystemUIOverlay] enum values that denotes
+  ///    the overlays to show.
   ///
   /// Return Value:
   ///
@@ -56,6 +77,29 @@ class SystemChrome {
   ///   If the overlay is unsupported on the platform, enabling or disabling
   ///   that overlay is a no-op and always return true.
   static Future<bool> setEnabledSystemUIOverlays(int overlaysMask) async {
-    return (await _systemChromeProxy.setEnabledSystemUiOverlays(overlaysMask)).success;
+    return (await _systemChromeProxy.setEnabledSystemUiOverlays(
+      overlaysMask)).success;
+  }
+
+  /// Specifies the style of the system overlays that are visible on the
+  /// embedder (if any). The embedder may choose to ignore unsupported
+  /// overlays.
+  ///
+  /// Arguments:
+  ///
+  ///  * [style]: A [SystemUiOverlayStyle] enum value denoting the style to use
+  ///
+  /// Return Value:
+  ///
+  ///   boolean indicating if the preference was conveyed successfully to the
+  ///   embedder.
+  ///
+  /// Platform Specific Notes:
+  ///
+  ///   If the overlay is unsupported on the platform, enabling or disabling
+  ///   that overlay is a no-op and always return true.
+  static Future<bool> setSystemUIOverlayStyle(SystemUiOverlayStyle style) async {
+    return (await _systemChromeProxy.setSystemUiOverlayStyle(
+      style)).success;
   }
 }

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

@@ -40,6 +40,7 @@ class WidgetsApp extends StatefulWidget {
     Key key,
     @required this.onGenerateRoute,
     this.title,
+    this.brightness,
     this.textStyle,
     this.color,
     this.navigatorObserver,
@@ -56,6 +57,9 @@ class WidgetsApp extends StatefulWidget {
   /// A one-line description of this app for use in the window manager.
   final String title;
 
+  /// The overall brightness of the app, describing its contrast needs.
+  final Brightness brightness;
+
   /// The default text style for [Text] in the application.
   final TextStyle textStyle;
 
@@ -180,6 +184,7 @@ class _WidgetsAppState extends State<WidgetsApp> implements WidgetsBindingObserv
           devicePixelRatio: ui.window.devicePixelRatio,
           child: new Title(
             title: config.title,
+            brightness: config.brightness,
             color: config.color,
             child: new Navigator(
               key: _navigator,

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

@@ -415,6 +415,21 @@ class ClipPath extends SingleChildRenderObjectWidget {
   }
 }
 
+/// Describes the contrast needs of a color.
+enum Brightness {
+  /// The color is dark and will require a light text color to achieve readable
+  /// contrast.
+  ///
+  /// For example, the color might be dark grey, requiring white text.
+  dark,
+
+  /// The color is light and will require a dark text color to achieve readable
+  /// contrast.
+  ///
+  /// For example, the color might be bright white, requiring black text.
+  light,
+}
+
 
 // POSITIONING AND SIZING NODES
 

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

@@ -4,6 +4,7 @@
 
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
+import 'package:sky_services/flutter/platform/system_chrome.mojom.dart' as mojom;
 
 /// A widget that describes this app in the operating system.
 class Title extends StatelessWidget {
@@ -11,6 +12,7 @@ class Title extends StatelessWidget {
   Title({
     Key key,
     this.title,
+    this.brightness,
     this.color,
     this.child
   }) : super(key: key) {
@@ -20,6 +22,9 @@ class Title extends StatelessWidget {
   /// A one-line description of this app for use in the window manager.
   final String title;
 
+  /// The brightness against which the window manager should render system text.
+  final Brightness brightness;
+
   /// A color that the window manager should use to identify this app.
   final Color color;
 
@@ -28,10 +33,22 @@ class Title extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    _updateSystemChrome();
     updateTaskDescription(label: title, color: color);
     return child;
   }
 
+  /// Updates the system chrome settings based on this title's metadata.
+  void _updateSystemChrome() {
+    // TODO(tvolkert): This may result in a decent amount of unnecessary
+    // overhead in the embedder (on every build). Consider making Title
+    // a StatefulWidget that only calls into the SystemChrome service when
+    // it sees that a value has changed.
+    SystemChrome.setSystemUIOverlayStyle(brightness == Brightness.dark
+        ? mojom.SystemUiOverlayStyle.light
+        : mojom.SystemUiOverlayStyle.dark);
+  }
+
   @override
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);