[web] Bootstrap tests without implicit view by default (flutter#48629)

- Follow up tests for flutter#48505
    - Tests for navigation without an implicit view should work.
- Package [this workaround](https://github.com/flutter/engine/blob/cd1a3b45d21e27b27ae711c561fb5a5f2679074f/lib/web_ui/test/engine/semantics/semantics_multi_view_test.dart#L29-L30) behind a nice, future-proof API.
- Tests by default start with no implicit view.
    - Tests that need an implicit view have to explicitly indicate so (by using the `withImplicitView` param).

Fixes flutter/flutter#138906

Author: mdebbar

lib/web_ui/lib/ui_web/src/ui_web/testing.dart

@@ -31,9 +31,9 @@ bool get debugEmulateFlutterTesterEnvironment =>
 set debugEmulateFlutterTesterEnvironment(bool value) {
   _debugEmulateFlutterTesterEnvironment = value;
   if (_debugEmulateFlutterTesterEnvironment) {
-    ensureImplicitViewInitialized();
     const ui.Size logicalSize = ui.Size(800.0, 600.0);
-    window.debugPhysicalSizeOverride = logicalSize * window.devicePixelRatio;
+    final EngineFlutterWindow? implicitView = EnginePlatformDispatcher.instance.implicitView;
+    implicitView?.debugPhysicalSizeOverride = logicalSize * implicitView.devicePixelRatio;
   }
   debugDisableFontFallbacks = value;
 }

lib/web_ui/test/canvaskit/backdrop_filter_golden_test.dart

@@ -17,7 +17,7 @@ const ui.Rect region = ui.Rect.fromLTRB(0, 0, 500, 500);
 
 void testMain() {
   group('BackdropFilter', () {
-    setUpCanvasKitTest();
+    setUpCanvasKitTest(withImplicitView: true);
     EngineFlutterDisplay.instance.debugOverrideDevicePixelRatio(1.0);
 
     test('blur renders to the edges', () async {

lib/web_ui/test/canvaskit/canvas_golden_test.dart

@@ -21,7 +21,7 @@ const ui.Rect kDefaultRegion = ui.Rect.fromLTRB(0, 0, 500, 250);
 
 void testMain() {
   group('CkCanvas', () {
-    setUpCanvasKitTest();
+    setUpCanvasKitTest(withImplicitView: true);
 
     setUp(() {
       renderer.fontCollection.debugResetFallbackFonts();

lib/web_ui/test/canvaskit/color_filter_golden_test.dart

@@ -17,7 +17,7 @@ const ui.Rect region = ui.Rect.fromLTRB(0, 0, 500, 250);
 
 void testMain() {
   group('ColorFilter', () {
-    setUpCanvasKitTest();
+    setUpCanvasKitTest(withImplicitView: true);
 
     test('ColorFilter.matrix applies a color filter', () async {
       final LayerSceneBuilder builder = LayerSceneBuilder();

lib/web_ui/test/canvaskit/common.dart

@@ -19,8 +19,9 @@ export '../common/rendering.dart' show renderScene;
 const MethodCodec codec = StandardMethodCodec();
 
 /// Common test setup for all CanvasKit unit-tests.
-void setUpCanvasKitTest() {
+void setUpCanvasKitTest({bool withImplicitView = false}) {
   setUpUnitTests(
+    withImplicitView: withImplicitView,
     emulateTesterEnvironment: false,
     setUpTestViewDimensions: false,
   );

lib/web_ui/test/canvaskit/display_canvas_factory_test.dart

@@ -30,7 +30,7 @@ class DummyDisplayCanvas extends DisplayCanvas {
 
 void testMain() {
   group('$DisplayCanvasFactory', () {
-    setUpCanvasKitTest();
+    setUpCanvasKitTest(withImplicitView: true);
 
     test('getCanvas', () {
       final DisplayCanvasFactory<DisplayCanvas> factory =

lib/web_ui/test/canvaskit/embedded_views_test.dart

@@ -25,7 +25,7 @@ void main() {
 
 void testMain() {
   group('$HtmlViewEmbedder', () {
-    setUpCanvasKitTest();
+    setUpCanvasKitTest(withImplicitView: true);
 
     setUp(() {
       EngineFlutterDisplay.instance.debugOverrideDevicePixelRatio(1);

lib/web_ui/test/canvaskit/filter_test.dart

@@ -49,7 +49,7 @@ void testMain() {
     return filters;
   }
 
-  setUpCanvasKitTest();
+  setUpCanvasKitTest(withImplicitView: true);
 
   group('ImageFilters', () {
     test('can be constructed', () {

lib/web_ui/test/canvaskit/flutter_tester_emulation_golden_test.dart

@@ -20,7 +20,7 @@ void testMain() {
   ui_web.debugEmulateFlutterTesterEnvironment = true;
 
   group('flutter_tester emulation', () {
-    setUpCanvasKitTest();
+    setUpCanvasKitTest(withImplicitView: true);
 
     test('defaults to FlutterTest font family',
         () async {

lib/web_ui/test/canvaskit/frame_timings_test.dart

@@ -14,7 +14,7 @@ void main() {
 
 void testMain() {
   group('frame timings', () {
-    setUpCanvasKitTest();
+    setUpCanvasKitTest(withImplicitView: true);
 
     test('collects frame timings', () async {
       await runFrameTimingsTest();