Dispose of DOMTimer upon explicit ExecutionContext unregistration.

Source/core/frame/DOMTimer.cpp

 /*
  * Copyright (C) 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 90 matching lines @@
     if (singleShot)
         startOneShot(intervalMilliseconds, FROM_HERE);
     else
         startRepeating(intervalMilliseconds, FROM_HERE);
 }
 
 DOMTimer::~DOMTimer()
 {
 }
 
+void DOMTimer::dispose()
+{
+    m_action = nullptr;
+    m_userGestureToken = nullptr;
+    stop();
+}
+
 int DOMTimer::timeoutID() const
 {
     return m_timeoutID;
 }
 
 void DOMTimer::fired()
 {
     ExecutionContext* context = executionContext();
     context->setTimerNestingLevel(m_nestingLevel);
     ASSERT(!context->activeDOMObjectsAreSuspended());
@@ skipping 85 matching lines @@
         if (fireTime - alignedTimeRoundedDown < minimumInterval)
             return alignedTimeRoundedDown;
 
         return alignedTimeRoundedUp;
     }
 
     return fireTime;
 }
 
 } // namespace blink