Add MediaQuery.systemGestureInsets to support Android Q (#37416)

* Wire Window.systemGestureInsets to MediaQuery.systemGestureInsets

* Add systemGestureInsets property to TestWindow

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

@@ -93,6 +93,7 @@ class MediaQueryData {
     this.platformBrightness = Brightness.light,
     this.padding = EdgeInsets.zero,
     this.viewInsets = EdgeInsets.zero,
+    this.systemGestureInsets = EdgeInsets.zero,
     this.viewPadding = EdgeInsets.zero,
     this.physicalDepth = double.maxFinite,
     this.alwaysUse24HourFormat = false,
@@ -117,6 +118,7 @@ class MediaQueryData {
       padding = EdgeInsets.fromWindowPadding(window.padding, window.devicePixelRatio),
       viewPadding = EdgeInsets.fromWindowPadding(window.viewPadding, window.devicePixelRatio),
       viewInsets = EdgeInsets.fromWindowPadding(window.viewInsets, window.devicePixelRatio),
+      systemGestureInsets = EdgeInsets.fromWindowPadding(window.systemGestureInsets, window.devicePixelRatio),
       physicalDepth = window.physicalDepth,
       accessibleNavigation = window.accessibilityFeatures.accessibleNavigation,
       invertColors = window.accessibilityFeatures.invertColors,
@@ -215,6 +217,61 @@ class MediaQueryData {
   ///   property and how it relates to [padding] and [viewInsets].
   final EdgeInsets viewPadding;
 
+  /// The areas along the edges of the display where the system consumes
+  /// certain input events and blocks delivery of those events to the app.
+  ///
+  /// Starting with Android Q, simple swipe gestures that start within the
+  /// [systemGestureInsets] areas are used by the system for page navigation
+  /// and may not be delivered to the app. Taps and swipe gestures that begin
+  /// with a long-press are delivered to the app, but simple press-drag-release
+  /// swipe gestures which begin within the area defined by [systemGestureInsets]
+  /// may not be.
+  ///
+  /// Apps should avoid locating gesture detectors within the system gesture
+  /// insets area. Apps should feel free to put visual elements within
+  /// this area.
+  ///
+  /// This property is currently only expected to be set to a non-default value
+  /// on Android starting with version Q.
+  ///
+  /// {@tool snippet --template=stateful_widget_material}
+  ///
+  /// For apps that might be deployed on Android Q devices with full gesture
+  /// navigation enabled, use [MediaQuery.systemGestureInsets] with [Padding]
+  /// to avoid having the left and right edges of the [Slider] from appearing
+  /// within the area reserved for system gesture navigation.
+  ///
+  /// By default, [Slider]s expand to fill the available width. So, we pad the
+  /// left and right sides.
+  ///
+  /// ```dart
+  /// double _currentValue = 0.2;
+  ///
+  /// @override
+  /// Widget build(BuildContext context) {
+  ///   EdgeInsets systemGestureInsets = MediaQuery.of(context).systemGestureInsets;
+  ///   return Scaffold(
+  ///     appBar: AppBar(title: Text('Pad Slider to avoid systemGestureInsets')),
+  ///     body: Padding(
+  ///       padding: EdgeInsets.only( // only left and right padding are needed here
+  ///         left: systemGestureInsets.left,
+  ///         right: systemGestureInsets.right,
+  ///       ),
+  ///       child: Slider(
+  ///         value: _currentValue.toDouble(),
+  ///         onChanged: (double newValue) {
+  ///           setState(() {
+  ///             _currentValue = newValue;
+  ///           });
+  ///         },
+  ///       ),
+  ///     ),
+  ///   );
+  /// }
+  /// ```
+  /// {@end-tool}
+  final EdgeInsets systemGestureInsets;
+
   /// The physical depth is the maximum elevation that the Window allows.
   ///
   /// Physical layers drawn at or above this elevation will have their elevation
@@ -300,6 +357,7 @@ class MediaQueryData {
     EdgeInsets padding,
     EdgeInsets viewPadding,
     EdgeInsets viewInsets,
+    EdgeInsets systemGestureInsets,
     double physicalDepth,
     bool alwaysUse24HourFormat,
     bool highContrast,
@@ -316,6 +374,7 @@ class MediaQueryData {
       padding: padding ?? this.padding,
       viewPadding: viewPadding ?? this.viewPadding,
       viewInsets: viewInsets ?? this.viewInsets,
+      systemGestureInsets: systemGestureInsets ?? this.systemGestureInsets,
       physicalDepth: physicalDepth ?? this.physicalDepth,
       alwaysUse24HourFormat: alwaysUse24HourFormat ?? this.alwaysUse24HourFormat,
       invertColors: invertColors ?? this.invertColors,

packages/flutter/test/widgets/media_query_test.dart

@@ -59,6 +59,7 @@ void main() {
     expect(copied.padding, data.padding);
     expect(copied.viewPadding, data.viewPadding);
     expect(copied.viewInsets, data.viewInsets);
+    expect(copied.systemGestureInsets, data.systemGestureInsets);
     expect(copied.physicalDepth, data.physicalDepth);
     expect(copied.alwaysUse24HourFormat, data.alwaysUse24HourFormat);
     expect(copied.accessibleNavigation, data.accessibleNavigation);
@@ -77,6 +78,7 @@ void main() {
       padding: const EdgeInsets.all(9.10938),
       viewPadding: const EdgeInsets.all(11.24031),
       viewInsets: const EdgeInsets.all(1.67262),
+      systemGestureInsets: const EdgeInsets.all(1.5556),
       physicalDepth: 120.0,
       alwaysUse24HourFormat: true,
       accessibleNavigation: true,
@@ -91,6 +93,7 @@ void main() {
     expect(copied.padding, const EdgeInsets.all(9.10938));
     expect(copied.viewPadding, const EdgeInsets.all(11.24031));
     expect(copied.viewInsets, const EdgeInsets.all(1.67262));
+    expect(copied.systemGestureInsets, const EdgeInsets.all(1.5556));
     expect(copied.physicalDepth, 120.0);
     expect(copied.alwaysUse24HourFormat, true);
     expect(copied.accessibleNavigation, true);

packages/flutter_test/lib/src/window.dart

@@ -148,6 +148,20 @@ class TestWindow implements Window {
     onMetricsChanged();
   }
 
+  @override
+  WindowPadding get systemGestureInsets => _systemGestureInsetsTestValue ?? _window.systemGestureInsets;
+  WindowPadding _systemGestureInsetsTestValue;
+  /// Hides the real system gesture insets and reports the given [systemGestureInsetsTestValue] instead.
+  set systemGestureInsetsTestValue(WindowPadding systemGestureInsetsTestValue) {
+    _systemGestureInsetsTestValue = systemGestureInsetsTestValue;
+    onMetricsChanged();
+  }
+  /// Deletes any existing test system gesture insets and returns to using the real system gesture insets.
+  void clearSystemGestureInsetsTestValue() {
+    _systemGestureInsetsTestValue = null;
+    onMetricsChanged();
+  }
+
   @override
   VoidCallback get onMetricsChanged => _window.onMetricsChanged;
   @override