Add a new API for testing animated images

Source/core/svg/animation/SMILTimeContainer.h

 /*
  * Copyright (C) 2008 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 51 matching lines @@
     void begin();
     void pause();
     void resume();
     void setElapsed(SMILTime);
 
     void serviceAnimations(double monotonicAnimationStartTime);
     bool hasAnimations() const;
 
     void setDocumentOrderIndexesDirty() { m_documentOrderIndexesDirty = true; }
 
+    // Advance the animation timeline a single frame.
+    void advanceFrameForTesting();
+
     DECLARE_TRACE();
 
 private:
     explicit SMILTimeContainer(SVGSVGElement& owner);
 
     enum FrameSchedulingState {
         // No frame scheduled.
         Idle,
         // Scheduled a wakeup to update the animation values.
         SynchronizeAnimations,
@@ skipping 53 matching lines @@
 
     RawPtrWillBeMember<SVGSVGElement> m_ownerSVGElement;
 
 #if ENABLE(ASSERT)
     bool m_preventScheduledAnimationsChanges;
 #endif
 };
 }
 
 #endif // SMILTimeContainer_h