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

Source/core/animation/AnimationClock.h

 /*
  * 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 32 matching lines @@
 public:
     explicit AnimationClock(WTF::TimeFunction monotonicallyIncreasingTime = WTF::monotonicallyIncreasingTime)
         : m_monotonicallyIncreasingTime(monotonicallyIncreasingTime)
         , m_time(0)
         , m_currentTask(std::numeric_limits<unsigned>::max())
     {
     }
 
     void updateTime(double time);
     double currentTime();
-    void resetTimeForTesting();
+    void resetTimeForTesting(double time = 0);
 
     static void notifyTaskStart() { ++s_currentTask; }
 
 private:
     WTF::TimeFunction m_monotonicallyIncreasingTime;
     double m_time;
     unsigned m_currentTask;
     static unsigned s_currentTask;
 };
 
 } // namespace blink
 
 #endif // AnimationClock_h