FlutterCompositor should not call present callback if there are no layers

Author: knopp

shell/platform/darwin/macos/framework/Source/FlutterCompositor.h

@@ -73,7 +73,7 @@ class FlutterCompositor {
 
   // Calls the present callback and ensures the frame status is updated
   // to frame ended, returning whether the present was successful or not.
-  bool EndFrame();
+  bool EndFrame(bool have_layers);
 
   // Creates a CALayer object which is backed by the supplied IOSurface, and
   // adds it to the root CALayer for this FlutterViewController's view.

shell/platform/darwin/macos/framework/Source/FlutterCompositor.mm

@@ -29,8 +29,8 @@
   SetFrameStatus(FrameStatus::kStarted);
 }
 
-bool FlutterCompositor::EndFrame() {
-  bool status = present_callback_();
+bool FlutterCompositor::EndFrame(bool have_layers) {
+  bool status = have_layers ? present_callback_() : true;
   SetFrameStatus(FrameStatus::kEnded);
   return status;
 }

shell/platform/darwin/macos/framework/Source/FlutterGLCompositor.mm

@@ -102,7 +102,7 @@
     };
   }
 
-  return EndFrame();
+  return EndFrame(layers_count > 0);
 }
 
 }  // namespace flutter

shell/platform/darwin/macos/framework/Source/FlutterMetalCompositor.mm

@@ -97,7 +97,7 @@
     };
   }
 
-  return EndFrame();
+  return EndFrame(layers_count > 0);
 }
 
 }  // namespace flutter

shell/platform/darwin/macos/framework/Source/FlutterSurfaceManager.mm

@@ -58,6 +58,13 @@ - (void)ensureSurfaceSize:(CGSize)size {
 }
 
 - (void)swapBuffers {
+#ifndef NDEBUG
+  // swapBuffers should not be called unless a frame was drawn
+  @synchronized(self) {
+    assert(_frameInProgress);
+  }
+#endif
+
   _contentLayer.frame = _containingLayer.bounds;
   _contentLayer.transform = _contentTransform;
   IOSurfaceRef contentIOSurface = [_ioSurfaces[kFlutterSurfaceManagerBackBuffer] ioSurface];