Revert of Web Animations: Timeline should not advance during task execution

Source/core/animation/css/TransitionTimeline.cpp

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 27 matching lines @@
 
 PassRefPtr<TransitionTimeline> TransitionTimeline::create(Document* document, PassOwnPtr<PlatformTiming> timing)
 {
     return adoptRef(new TransitionTimeline(document, timing));
 }
 
 TransitionTimeline::TransitionTimeline(Document* document, PassOwnPtr<PlatformTiming> timing)
     : DocumentTimeline(document, timing)
 {
     setZeroTime(document->animationClock().currentTime());
+    document->animationClock().unfreeze();
 }
 
 } // namespace WebCore