Merge remote-tracking branch 'origin/main' into reland-3-mv-pipeline

lib/ui/platform_dispatcher.dart

@@ -811,11 +811,12 @@ class PlatformDispatcher {
   /// Schedule a frame to run as soon as possible, rather than waiting for the
   /// engine to request a frame in response to a system "Vsync" signal.
   ///
-  /// This method is used during application startup so that the first frame
-  /// (which is likely to be quite expensive) can start a few extra milliseconds
-  /// earlier. Using it in other situations might lead to unintended results,
-  /// such as screen tearing. Depending on platforms and situations, the warm up
-  /// frame might or might not be actually rendered onto the screen.
+  /// The application can call this method as soon as it starts up so that the
+  /// first frame (which is likely to be quite expensive) can start a few extra
+  /// milliseconds earlier. Using it in other situations might lead to
+  /// unintended results, such as screen tearing. Depending on platforms and
+  /// situations, the warm up frame might or might not be actually rendered onto
+  /// the screen.
   ///
   /// For more introduction to the warm up frame, see
   /// [SchedulerBinding.scheduleWarmUpFrame].

lib/web_ui/lib/src/engine/platform_dispatcher.dart

@@ -786,6 +786,12 @@ class EnginePlatformDispatcher extends ui.PlatformDispatcher {
   void scheduleWarmUpFrame({required ui.VoidCallback beginFrame, required ui.VoidCallback drawFrame}) {
     Timer.run(beginFrame);
     // We use timers here to ensure that microtasks flush in between.
+    //
+    // TODO(dkwingsmt): This logic was moved from the framework and is different
+    // from how Web renders a regular frame, which doesn't flush microtasks
+    // between the callbacks at all (see `initializeEngineServices`). We might
+    // want to change this. See the to-do in `initializeEngineServices` and
+    // https://github.com/flutter/engine/pull/50570#discussion_r1496671676
     Timer.run(drawFrame);
   }
 

lib/web_ui/test/engine/platform_dispatcher/platform_dispatcher_test.dart

@@ -418,32 +418,21 @@ void testMain() {
       expect(dispatcher.accessibilityPlaceholder.isConnected, isFalse);
     });
 
-
-    test('scheduleWarmupFrame should call both callbacks and flush microtasks', () async {
-      bool microtaskFlushed = false;
+    test('scheduleWarmupFrame should call both callbacks', () async {
       bool beginFrameCalled = false;
       final Completer<void> drawFrameCalled = Completer<void>();
       dispatcher.scheduleWarmUpFrame(beginFrame: () {
-        expect(microtaskFlushed, false);
         expect(drawFrameCalled.isCompleted, false);
         expect(beginFrameCalled, false);
         beginFrameCalled = true;
-        scheduleMicrotask(() {
-          expect(microtaskFlushed, false);
-          expect(drawFrameCalled.isCompleted, false);
-          microtaskFlushed = true;
-        });
-        expect(microtaskFlushed, false);
       }, drawFrame: () {
         expect(beginFrameCalled, true);
-        expect(microtaskFlushed, true);
         expect(drawFrameCalled.isCompleted, false);
         drawFrameCalled.complete();
       });
       await drawFrameCalled.future;
       expect(beginFrameCalled, true);
       expect(drawFrameCalled.isCompleted, true);
-      expect(microtaskFlushed, true);
     });
   });
 }

shell/common/engine_unittests.cc

@@ -339,7 +339,6 @@ class EngineContext {
   fml::WeakPtr<IOManager> io_manager_;
   fml::TaskRunnerAffineWeakPtr<SnapshotDelegate> snapshot_delegate_;
 };
-
 }  // namespace
 
 TEST_F(EngineTest, Create) {