If a compositing update is declared as needed, scheduleAnimation should be triggered.

Source/core/testing/Internals.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 254 matching lines @@
 
     [RaisesException] DOMString getImageSourceURL(Element element);
 
     boolean isSelectPopupVisible(Node node);
 
     [RaisesException] ClientRect selectionBounds();
 
     boolean loseSharedGraphicsContext3D();
 
     [RaisesException] void forceCompositingUpdate(Document document);
+    [RaisesException] boolean isCompositorFramePending(Document document);
 
     void setZoomFactor(float factor);
 
     [RaisesException] void setShouldRevealPassword(Element element, boolean reveal);
 
     [CallWith=ExecutionContext] Promise addOneToPromise(Promise promise);
 };