Web Animations: Set the DocumentTimeline's zero time when the Document reaches the 'loading' phase

Source/core/animation/css/CSSAnimations.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 171 matching lines @@
                 inactive.remove(animationName.impl());
                 continue;
             }
 
             KeyframeAnimationEffect::KeyframeVector keyframes;
             element->document()->styleResolver()->resolveKeyframes(element, style, animationName.impl(), keyframes);
             if (!keyframes.isEmpty()) {
                 Timing timing;
                 timingFromAnimationData(animationData, timing);
                 OwnPtr<CSSAnimations::EventDelegate> eventDelegate = adoptPtr(new EventDelegate(element, animationName));
+                ASSERT(!isNull(element->document()->timeline()->currentTime()));
                 // FIXME: crbug.com/268791 - Keyframes are already normalized, perhaps there should be a flag on KeyframeAnimationEffect to skip normalization.
                 m_animations.set(animationName.impl(), element->document()->timeline()->play(
                     Animation::create(element, KeyframeAnimationEffect::create(keyframes), timing, eventDelegate.release()).get()).get());
             }
         }
     }
 
     for (HashSet<StringImpl*>::const_iterator iter = inactive.begin(); iter != inactive.end(); ++iter)
         m_animations.take(*iter)->cancel();
 }
@@ skipping 28 matching lines @@
         maybeDispatch(Document::ANIMATIONITERATION_LISTENER, eventNames().webkitAnimationIterationEvent, elapsedTime);
         return;
     }
     if (wasInPlay && !isInPlay) {
         maybeDispatch(Document::ANIMATIONEND_LISTENER, eventNames().webkitAnimationEndEvent, elapsedTime);
         return;
     }
 }
 
 } // namespace WebCore