Web Animations CSS: Unfreeze AnimationClock if sampling timelines does not trigger style recalc

Source/core/animation/DocumentTimeline.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 68 matching lines @@
 
 void DocumentTimeline::serviceAnimations(double monotonicAnimationStartTime)
 {
     TRACE_EVENT0("webkit", "DocumentTimeline::serviceAnimations");
 
     m_timing->cancelWake();
 
     m_document->animationClock().updateTime(monotonicAnimationStartTime);
 
     double timeToNextEffect = std::numeric_limits<double>::infinity();
-    double playerNextEffect;
+    bool didTriggerStyleRecalc = false;
     for (int i = m_players.size() - 1; i >= 0; --i) {
-        if (!m_players[i]->update(&playerNextEffect))
+        double playerNextEffect;
+        bool playerDidTriggerStyleRecalc;
+        if (!m_players[i]->update(&playerNextEffect, &playerDidTriggerStyleRecalc))
             m_players.remove(i);
+        didTriggerStyleRecalc |= playerDidTriggerStyleRecalc;
         if (playerNextEffect < timeToNextEffect)
             timeToNextEffect = playerNextEffect;
     }
 
+    if (!didTriggerStyleRecalc)
+        m_document->animationClock().unfreeze();
+
     if (!m_players.isEmpty()) {
         if (timeToNextEffect < s_minimumDelay)
             m_timing->serviceOnNextFrame();
         else if (timeToNextEffect != std::numeric_limits<double>::infinity())
             m_timing->wakeAfter(timeToNextEffect - s_minimumDelay);
     }
 
     if (m_document->view() && !m_players.isEmpty())
         m_document->view()->scheduleAnimation();
 }
@@ skipping 43 matching lines @@
 }
 
 size_t DocumentTimeline::numberOfActiveAnimationsForTesting() const
 {
     // Includes all players whose directly associated timed items
     // are current or in effect.
     return isNull(m_zeroTime) ? 0 : m_players.size();
 }
 
 } // namespace