Skip invalid renders in Dart (flutter#47323)

With this PR, invalid renders are skipped in Dart in both release build and debug build.

Part of flutter/flutter#137073 and part of relanding flutter#45555.

Unit tests will be relanded in a following PR once this PR is confirmed performance-safe.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

lib/ui/platform_dispatcher.dart

@@ -308,9 +308,8 @@ class PlatformDispatcher {
     _invoke(onMetricsChanged, _onMetricsChangedZone);
   }
 
-  // A debug-only variable that stores the [FlutterView]s for which
-  // [FlutterView.render] has already been called during the current
-  // [onBeginFrame]/[onDrawFrame] callback sequence.
+  // The [FlutterView]s for which [FlutterView.render] has already been called
+  // during the current [onBeginFrame]/[onDrawFrame] callback sequence.
   //
   // It is null outside the scope of those callbacks indicating that calls to
   // [FlutterView.render] must be ignored. Furthermore, if a given [FlutterView]
@@ -320,16 +319,9 @@ class PlatformDispatcher {
   // Between [onBeginFrame] and [onDrawFrame] the properties value is
   // temporarily stored in `_renderedViewsBetweenCallbacks` so that it survives
   // the gap between the two callbacks.
-  //
-  // In release build, this variable is null, and therefore the calling rule is
-  // not enforced. This is because the check might hurt cold startup delay;
-  // see https://github.com/flutter/engine/pull/46919.
-  Set<FlutterView>? _debugRenderedViews;
-  // A debug-only variable that temporarily stores the `_renderedViews` value
-  // between `_beginFrame` and `_drawFrame`.
-  //
-  // In release build, this variable is null.
-  Set<FlutterView>? _debugRenderedViewsBetweenCallbacks;
+  Set<FlutterView>? _renderedViews;
+  // The `_renderedViews` value between `_beginFrame` and `_drawFrame`.
+  Set<FlutterView>? _renderedViewsBetweenCallbacks;
 
   /// A callback invoked when any view begins a frame.
   ///
@@ -351,26 +343,20 @@ class PlatformDispatcher {
 
   // Called from the engine, via hooks.dart
   void _beginFrame(int microseconds) {
-    assert(_debugRenderedViews == null);
-    assert(_debugRenderedViewsBetweenCallbacks == null);
-    assert(() {
-      _debugRenderedViews = <FlutterView>{};
-      return true;
-    }());
+    assert(_renderedViews == null);
+    assert(_renderedViewsBetweenCallbacks == null);
+    _renderedViews = <FlutterView>{};
 
     _invoke1<Duration>(
       onBeginFrame,
       _onBeginFrameZone,
       Duration(microseconds: microseconds),
     );
 
-    assert(_debugRenderedViews != null);
-    assert(_debugRenderedViewsBetweenCallbacks == null);
-    assert(() {
-      _debugRenderedViewsBetweenCallbacks = _debugRenderedViews;
-      _debugRenderedViews = null;
-      return true;
-    }());
+    assert(_renderedViews != null);
+    assert(_renderedViewsBetweenCallbacks == null);
+    _renderedViewsBetweenCallbacks = _renderedViews;
+    _renderedViews = null;
   }
 
   /// A callback that is invoked for each frame after [onBeginFrame] has
@@ -388,22 +374,16 @@ class PlatformDispatcher {
 
   // Called from the engine, via hooks.dart
   void _drawFrame() {
-    assert(_debugRenderedViews == null);
-    assert(_debugRenderedViewsBetweenCallbacks != null);
-    assert(() {
-      _debugRenderedViews = _debugRenderedViewsBetweenCallbacks;
-      _debugRenderedViewsBetweenCallbacks = null;
-      return true;
-    }());
+    assert(_renderedViews == null);
+    assert(_renderedViewsBetweenCallbacks != null);
+    _renderedViews = _renderedViewsBetweenCallbacks;
+    _renderedViewsBetweenCallbacks = null;
 
     _invoke(onDrawFrame, _onDrawFrameZone);
 
-    assert(_debugRenderedViews != null);
-    assert(_debugRenderedViewsBetweenCallbacks == null);
-    assert(() {
-      _debugRenderedViews = null;
-      return true;
-    }());
+    assert(_renderedViews != null);
+    assert(_renderedViewsBetweenCallbacks == null);
+    _renderedViews = null;
   }
 
   /// A callback that is invoked when pointer data is available.

lib/ui/window.dart

@@ -355,14 +355,10 @@ class FlutterView {
   ///   painting.
   void render(Scene scene) {
     // Duplicated calls or calls outside of onBeginFrame/onDrawFrame (indicated
-    // by _debugRenderedViews being null) are ignored. See _debugRenderedViews.
+    // by _renderedViews being null) are ignored. See _renderedViews.
     // TODO(dkwingsmt): We should change this skip into an assertion.
     // https://github.com/flutter/flutter/issues/137073
-    bool validRender = true;
-    assert(() {
-      validRender = platformDispatcher._debugRenderedViews?.add(this) ?? false;
-      return true;
-    }());
+    final bool validRender = platformDispatcher._renderedViews?.add(this) ?? false;
     if (validRender) {
       _render(viewId, scene as _NativeScene);
     }

shell/common/animator.cc

@@ -179,15 +179,7 @@ void Animator::EndFrame() {
 void Animator::Render(int64_t view_id,
                       std::unique_ptr<flutter::LayerTree> layer_tree,
                       float device_pixel_ratio) {
-  // Animator::Render should be called between BeginFrame and EndFrame,
-  // which is indicated by frame_timings_recorder_ being non-null.
-  // This might happen on release build, and is guarded by PlatformDispatcher on
-  // debug build.
-  // TODO(dkwingsmt): We should change this skip into an assertion.
-  // https://github.com/flutter/flutter/issues/137073
-  if (frame_timings_recorder_ == nullptr) {
-    return;
-  }
+  FML_CHECK(frame_timings_recorder_ != nullptr);
 
   has_rendered_ = true;
 

shell/common/animator.h

@@ -58,7 +58,8 @@ class Animator final {
   ///
   ///           This method must be called during a vsync callback, or
   ///           technically, between Animator::BeginFrame and Animator::EndFrame
-  ///           (both private methods). Otherwise, this call will be ignored.
+  ///           (both private methods). Otherwise, an assertion will be
+  ///           triggered.
   ///
   void Render(int64_t view_id,
               std::unique_ptr<flutter::LayerTree> layer_tree,