Web Animations: Zero time of the document timeline should correspond with navigationStart

Source/core/animation/AnimationClock.cpp

 /*
  * Copyright (c) 2014, 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 54 matching lines @@
             ASSERT(newTime >= currentTime);
             ASSERT(newTime <= currentTime + approximateFrameTime);
             updateTime(newTime);
         } else {
             m_currentTask = s_currentTask;
         }
     }
     return m_time;
 }
 
-void AnimationClock::resetTimeForTesting()
+void AnimationClock::resetTimeForTesting(double time)
 {
-    m_time = 0;
+    m_time = time;
     m_currentTask = 0;
     s_currentTask = 0;
 }
 
 }