[a11y] Add breadcrumbs in unittests comments

Add breadcrumbs to make it easier to jump between the Dart fixture side
and the embedder side of the EmbedderA11yTest.A11yTreeIsConsistent
unittest.

Author: cbracken

shell/platform/embedder/fixtures/main.dart

@@ -124,23 +124,23 @@ Future<SemanticsActionData> get semanticsAction {
 
 @pragma('vm:entry-point')
 void a11y_main() async {
-  // Return initial state (semantics disabled).
+  // 1: Return initial state (semantics disabled).
   notifySemanticsEnabled(PlatformDispatcher.instance.semanticsEnabled);
 
-  // Await semantics enabled from embedder.
+  // 2: Await semantics enabled from embedder.
   await semanticsChanged;
   notifySemanticsEnabled(PlatformDispatcher.instance.semanticsEnabled);
 
-  // Return initial state of accessibility features.
+  // 3: Return initial state of accessibility features.
   notifyAccessibilityFeatures(
       PlatformDispatcher.instance.accessibilityFeatures.reduceMotion);
 
-  // Await accessibility features changed from embedder.
+  // 4: Await accessibility features changed from embedder.
   await accessibilityFeaturesChanged;
   notifyAccessibilityFeatures(
       PlatformDispatcher.instance.accessibilityFeatures.reduceMotion);
 
-  // Fire semantics update.
+  // 5: Fire semantics update.
   final SemanticsUpdateBuilder builder = SemanticsUpdateBuilder()
     ..updateNode(
       id: 42,
@@ -284,15 +284,15 @@ void a11y_main() async {
 
   signalNativeTest();
 
-  // Await semantics action from embedder.
+  // 6: Await semantics action from embedder.
   final SemanticsActionData data = await semanticsAction;
   final List<int> actionArgs = <int>[
     data.args!.getInt8(0),
     data.args!.getInt8(1)
   ];
   notifySemanticsAction(data.id, data.action.index, actionArgs);
 
-  // Await semantics disabled from embedder.
+  // 7: Await semantics disabled from embedder.
   await semanticsChanged;
   notifySemanticsEnabled(PlatformDispatcher.instance.semanticsEnabled);
 }

shell/platform/embedder/tests/embedder_a11y_unittests.cc

@@ -177,7 +177,7 @@ TEST_F(EmbedderA11yTest, A11yTreeIsConsistent) {
   auto engine = builder.LaunchEngine();
   ASSERT_TRUE(engine.is_valid());
 
-  // Wait for initial NotifySemanticsEnabled(false).
+  // 1: Wait for initial notifySemanticsEnabled(false).
   fml::AutoResetWaitableEvent notify_semantics_enabled_latch;
   notify_semantics_enabled_callback = [&](Dart_NativeArguments args) {
     Dart_Handle exception = nullptr;
@@ -188,17 +188,7 @@ TEST_F(EmbedderA11yTest, A11yTreeIsConsistent) {
   };
   notify_semantics_enabled_latch.Wait();
 
-  // Prepare to NotifyAccessibilityFeatures call
-  fml::AutoResetWaitableEvent notify_features_latch;
-  notify_accessibility_features_callback = [&](Dart_NativeArguments args) {
-    Dart_Handle exception = nullptr;
-    bool enabled =
-        ::tonic::DartConverter<bool>::FromArguments(args, 0, exception);
-    ASSERT_FALSE(enabled);
-    notify_features_latch.Signal();
-  };
-
-  // Enable semantics. Wait for NotifySemanticsEnabled(true).
+  // 2: Enable semantics. Wait for notifySemanticsEnabled(true).
   fml::AutoResetWaitableEvent notify_semantics_enabled_latch_2;
   notify_semantics_enabled_callback = [&](Dart_NativeArguments args) {
     Dart_Handle exception = nullptr;
@@ -211,10 +201,18 @@ TEST_F(EmbedderA11yTest, A11yTreeIsConsistent) {
   ASSERT_EQ(result, FlutterEngineResult::kSuccess);
   notify_semantics_enabled_latch_2.Wait();
 
-  // Wait for initial accessibility features (reduce_motion == false)
+  // 3: Wait for notifyAccessibilityFeatures (reduce_motion == false)
+  fml::AutoResetWaitableEvent notify_features_latch;
+  notify_accessibility_features_callback = [&](Dart_NativeArguments args) {
+    Dart_Handle exception = nullptr;
+    bool enabled =
+        ::tonic::DartConverter<bool>::FromArguments(args, 0, exception);
+    ASSERT_FALSE(enabled);
+    notify_features_latch.Signal();
+  };
   notify_features_latch.Wait();
 
-  // Set accessibility features: (reduce_motion == true)
+  // 4: Wait for notifyAccessibilityFeatures (reduce_motion == true)
   fml::AutoResetWaitableEvent notify_features_latch_2;
   notify_accessibility_features_callback = [&](Dart_NativeArguments args) {
     Dart_Handle exception = nullptr;
@@ -228,12 +226,12 @@ TEST_F(EmbedderA11yTest, A11yTreeIsConsistent) {
   ASSERT_EQ(result, FlutterEngineResult::kSuccess);
   notify_features_latch_2.Wait();
 
-  // Wait for UpdateSemantics callback on platform (current) thread.
+  // 5: Wait for UpdateSemantics callback on platform (current) thread.
   signal_native_latch.Wait();
   fml::MessageLoop::GetCurrent().RunExpiredTasksNow();
   semantics_update_latch.Wait();
 
-  // Dispatch a tap to semantics node 42. Wait for NotifySemanticsAction.
+  // 6: Dispatch a tap to semantics node 42. Wait for NotifySemanticsAction.
   fml::AutoResetWaitableEvent notify_semantics_action_latch;
   notify_semantics_action_callback = [&](Dart_NativeArguments args) {
     Dart_Handle exception = nullptr;
@@ -257,7 +255,7 @@ TEST_F(EmbedderA11yTest, A11yTreeIsConsistent) {
   ASSERT_EQ(result, FlutterEngineResult::kSuccess);
   notify_semantics_action_latch.Wait();
 
-  // Disable semantics. Wait for NotifySemanticsEnabled(false).
+  // 7: Disable semantics. Wait for NotifySemanticsEnabled(false).
   fml::AutoResetWaitableEvent notify_semantics_enabled_latch_3;
   notify_semantics_enabled_callback = [&](Dart_NativeArguments args) {
     Dart_Handle exception = nullptr;