Predictive back route transitions by default (flutter#165832)

This PR turns on predictive back route transitions by default on
supported Android devices.

With flutter#154718, the default
(PredictiveBackPageTransitionsBuilder) is the [shared element
transition](https://developer.android.com/design/ui/mobile/guides/patterns/predictive-back#shared-element-transition).
The [full screen
transition](https://developer.android.com/design/ui/mobile/guides/patterns/predictive-back#full-screen-surfaces)
is also available by using
PredictiveBackFullScreenPageTransitionsBuilder.

Original PR: flutter#146788

Depends on: flutter#154718

When this lands in stable, the docs should be updated:
https://docs.flutter.dev/platform-integration/android/predictive-back

Author: justinmc

examples/api/test/material/divider/divider.0_test.dart

@@ -13,7 +13,11 @@ void main() {
     expect(find.byType(Divider), findsOneWidget);
 
     // Divider is positioned horizontally.
-    final Offset container = tester.getBottomLeft(find.byType(ColoredBox).first);
+    final Offset container = tester.getBottomLeft(
+      find
+          .descendant(of: find.byType(example.DividerExample), matching: find.byType(ColoredBox))
+          .first,
+    );
     expect(container.dy, tester.getTopLeft(find.byType(Divider)).dy);
 
     final Offset subheader = tester.getTopLeft(find.text('Subheader'));

examples/api/test/widgets/basic/listener.0_test.dart

@@ -16,7 +16,14 @@ void main() {
 
     final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
     await gesture.addPointer();
-    await gesture.down(tester.getCenter(find.byType(ColoredBox)));
+    await gesture.down(
+      tester.getCenter(
+        find.descendant(
+          of: find.byType(example.ListenerExample),
+          matching: find.byType(ColoredBox),
+        ),
+      ),
+    );
     await tester.pump();
 
     expect(find.text('1 presses\n0 releases'), findsOneWidget);

examples/api/test/widgets/basic/mouse_region.0_test.dart

@@ -18,13 +18,28 @@ void main() {
 
     final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
     await gesture.addPointer();
-    await gesture.moveTo(tester.getCenter(find.byType(ColoredBox)));
+    await gesture.moveTo(
+      tester.getCenter(
+        find.descendant(
+          of: find.byType(example.MouseRegionExample),
+          matching: find.byType(ColoredBox),
+        ),
+      ),
+    );
     await tester.pump();
 
     expect(find.text('1 Entries\n0 Exits'), findsOneWidget);
     expect(find.text('The cursor is here: (400.00, 328.00)'), findsOneWidget);
 
-    await gesture.moveTo(tester.getCenter(find.byType(ColoredBox)) + const Offset(50.0, 30.0));
+    await gesture.moveTo(
+      tester.getCenter(
+            find.descendant(
+              of: find.byType(example.MouseRegionExample),
+              matching: find.byType(ColoredBox),
+            ),
+          ) +
+          const Offset(50.0, 30.0),
+    );
     await tester.pump();
 
     expect(find.text('The cursor is here: (450.00, 358.00)'), findsOneWidget);

examples/api/test/widgets/heroes/hero.0_test.dart

@@ -24,19 +24,19 @@ void main() {
     expect(heroSize.height.roundToDouble(), 60.0);
 
     // Jump to 50% into the transition.
-    await tester.pump(const Duration(milliseconds: 75)); // 25% of 300ms
+    await tester.pump(quarterTransition);
     heroSize = tester.getSize(find.byType(Container));
     expect(heroSize.width.roundToDouble(), 189.0);
     expect(heroSize.height.roundToDouble(), 146.0);
 
     // Jump to 75% into the transition.
-    await tester.pump(const Duration(milliseconds: 75)); // 25% of 300ms
+    await tester.pump(quarterTransition);
     heroSize = tester.getSize(find.byType(Container));
     expect(heroSize.width.roundToDouble(), 199.0);
     expect(heroSize.height.roundToDouble(), 190.0);
 
     // Jump to 100% into the transition.
-    await tester.pump(const Duration(milliseconds: 75)); // 25% of 300ms
+    await tester.pump(quarterTransition);
     heroSize = tester.getSize(find.byType(Container));
     expect(heroSize, const Size(200.0, 200.0));
 
@@ -45,25 +45,25 @@ void main() {
     await tester.pump();
 
     // Jump 25% into the transition (total length = 300ms)
-    await tester.pump(const Duration(milliseconds: 75)); // 25% of 300ms
+    await tester.pump(quarterTransition);
     heroSize = tester.getSize(find.byType(Container));
     expect(heroSize.width.roundToDouble(), 199.0);
     expect(heroSize.height.roundToDouble(), 190.0);
 
     // Jump to 50% into the transition.
-    await tester.pump(const Duration(milliseconds: 75)); // 25% of 300ms
+    await tester.pump(quarterTransition);
     heroSize = tester.getSize(find.byType(Container));
     expect(heroSize.width.roundToDouble(), 189.0);
     expect(heroSize.height.roundToDouble(), 146.0);
 
     // Jump to 75% into the transition.
-    await tester.pump(const Duration(milliseconds: 75)); // 25% of 300ms
+    await tester.pump(quarterTransition);
     heroSize = tester.getSize(find.byType(Container));
     expect(heroSize.width.roundToDouble(), 103.0);
     expect(heroSize.height.roundToDouble(), 60.0);
 
     // Jump to 100% into the transition.
-    await tester.pump(const Duration(milliseconds: 75)); // 25% of 300ms
+    await tester.pump(quarterTransition);
     heroSize = tester.getSize(find.byType(Container));
     expect(heroSize, const Size(50.0, 50.0));
   });

examples/api/test/widgets/transitions/align_transition.0_test.dart

@@ -9,7 +9,13 @@ import 'package:flutter_test/flutter_test.dart';
 void main() {
   testWidgets('Shows flutter logo in transition', (WidgetTester tester) async {
     await tester.pumpWidget(const example.AlignTransitionExampleApp());
-    expect(find.byType(ColoredBox), findsOneWidget);
+    expect(
+      find.descendant(
+        of: find.byType(example.AlignTransitionExample),
+        matching: find.byType(ColoredBox),
+      ),
+      findsOneWidget,
+    );
     expect(
       find.byWidgetPredicate(
         (Widget padding) => padding is Padding && padding.padding == const EdgeInsets.all(8.0),

examples/api/test/widgets/transitions/fade_transition.0_test.dart

@@ -13,16 +13,19 @@ void main() {
     await tester.pumpWidget(const example.FadeTransitionExampleApp());
 
     expect(
-      find.ancestor(of: find.byType(FlutterLogo), matching: find.byType(FadeTransition)),
+      find.descendant(
+        of: find.byType(example.FadeTransitionExample),
+        matching: find.byType(FadeTransition),
+      ),
       findsOneWidget,
     );
   });
 
   testWidgets('FadeTransition animates', (WidgetTester tester) async {
     await tester.pumpWidget(const example.FadeTransitionExampleApp());
 
-    final Finder fadeTransitionFinder = find.ancestor(
-      of: find.byType(FlutterLogo),
+    final Finder fadeTransitionFinder = find.descendant(
+      of: find.byType(example.FadeTransitionExample),
       matching: find.byType(FadeTransition),
     );
 

examples/api/test/widgets/transitions/slide_transition.0_test.dart

@@ -13,7 +13,13 @@ void main() {
     expect(find.byType(Center), findsOneWidget);
     expect(find.byType(FlutterLogo), findsOneWidget);
     expect(find.byType(Padding), findsAtLeast(1));
-    expect(find.byType(SlideTransition), findsOneWidget);
+    expect(
+      find.descendant(
+        of: find.byType(example.SlideTransitionExample),
+        matching: find.byType(SlideTransition),
+      ),
+      findsOneWidget,
+    );
   });
 
   testWidgets('Animates repeatedly every 2 seconds', (WidgetTester tester) async {

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

@@ -17,6 +17,7 @@ import 'package:flutter/services.dart';
 
 import 'color_scheme.dart';
 import 'colors.dart';
+import 'predictive_back_page_transitions_builder.dart';
 import 'theme.dart';
 
 // Slides the page upwards and fades it in, starting from 1/4 screen
@@ -759,7 +760,12 @@ class FadeForwardsPageTransitionsBuilder extends PageTransitionsBuilder {
   final Color? backgroundColor;
 
   /// The value of [transitionDuration] in milliseconds.
-  static const int kTransitionMilliseconds = 800;
+  ///
+  /// Eyeballed on a physical Pixel 9 running Android 16. This does not match
+  /// the actual value used by native Android, which is 800ms, because native
+  /// Android is using Material 3 Expressive springs that are not currently
+  /// supported by Flutter. So for now at least, this is an approximation.
+  static const int kTransitionMilliseconds = 450;
 
   @override
   Duration get transitionDuration => const Duration(milliseconds: kTransitionMilliseconds);
@@ -1097,7 +1103,7 @@ class PageTransitionsTheme with Diagnosticable {
 
   static const Map<TargetPlatform, PageTransitionsBuilder> _defaultBuilders =
       <TargetPlatform, PageTransitionsBuilder>{
-        TargetPlatform.android: ZoomPageTransitionsBuilder(),
+        TargetPlatform.android: PredictiveBackPageTransitionsBuilder(),
         TargetPlatform.iOS: CupertinoPageTransitionsBuilder(),
         TargetPlatform.macOS: CupertinoPageTransitionsBuilder(),
         TargetPlatform.windows: ZoomPageTransitionsBuilder(),

packages/flutter/test/material/bottom_app_bar_test.dart

@@ -191,7 +191,9 @@ void main() {
     final BottomAppBar bottomAppBar = tester.widget(find.byType(BottomAppBar));
     expect(bottomAppBar.padding, customPadding);
     final Rect babRect = tester.getRect(find.byType(BottomAppBar));
-    final Rect childRect = tester.getRect(find.byType(ColoredBox));
+    final Rect childRect = tester.getRect(
+      find.descendant(of: find.byType(BottomAppBar), matching: find.byType(ColoredBox)),
+    );
     expect(childRect, const Rect.fromLTRB(250, 530, 550, 590));
     expect(babRect, const Rect.fromLTRB(240, 520, 560, 600));
   });

packages/flutter/test/material/expansion_tile_test.dart

@@ -1690,7 +1690,9 @@ void main() {
       );
 
       final Size materialAppSize = tester.getSize(find.byType(MaterialApp));
-      final Size titleSize = tester.getSize(find.byType(ColoredBox));
+      final Size titleSize = tester.getSize(
+        find.descendant(of: find.byType(ExpansionTile), matching: find.byType(ColoredBox)),
+      );
 
       expect(titleSize.width, materialAppSize.width);
     },
@@ -1713,7 +1715,9 @@ void main() {
       );
 
       final Size materialAppSize = tester.getSize(find.byType(MaterialApp));
-      final Size titleSize = tester.getSize(find.byType(ColoredBox));
+      final Size titleSize = tester.getSize(
+        find.descendant(of: find.byType(ExpansionTile), matching: find.byType(ColoredBox)),
+      );
 
       expect(titleSize.width, materialAppSize.width - 32.0);
     },