Web Animations: Introduce ActiveAnimations and AnimationStack

Source/core/animation/TimedItem.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 @@
     : m_parent(0)
     , m_startTime(0)
     , m_specified(timing)
     , m_calculated()
 {
     timing.assertValid();
 }
 
 void TimedItem::updateInheritedTime(double inheritedTime) const
 {
+    ASSERT(player());
     const double localTime = inheritedTime - m_startTime;
     const double iterationDuration = m_specified.hasIterationDuration
         ? m_specified.iterationDuration
         : intrinsicIterationDuration();
 
     const double repeatedDuration = iterationDuration * m_specified.iterationCount;
     const double activeDuration = m_specified.playbackRate
         ? repeatedDuration / abs(m_specified.playbackRate)
         : std::numeric_limits<double>::infinity();
 
@@ skipping 42 matching lines @@
     , currentIteration(nullValue())
     , timeFraction(nullValue())
     , isScheduled(false)
     , isActive(false)
     , isCurrent(false)
     , isInEffect(false)
 {
 }
 
 } // namespace WebCore