Dispose of DOMTimer upon explicit ExecutionContext unregistration.

Source/core/dom/ExecutionContext.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2012 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:
  * 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
@@ skipping 187 matching lines @@
 
     timer->suspendIfNeeded();
 
     return timer->timeoutID();
 }
 
 void ExecutionContext::removeTimeoutByID(int timeoutID)
 {
     if (timeoutID <= 0)
         return;
+
+    if (DOMTimer* removedTimer = m_timeouts.get(timeoutID))
+        removedTimer->dispose();
+
     m_timeouts.remove(timeoutID);
 }
 
 PublicURLManager& ExecutionContext::publicURLManager()
 {
     if (!m_publicURLManager)
         m_publicURLManager = PublicURLManager::create(this);
     return *m_publicURLManager;
 }
 
@@ skipping 54 matching lines @@
 #if ENABLE(OILPAN)
     visitor->trace(m_pendingExceptions);
     visitor->trace(m_publicURLManager);
     visitor->trace(m_timeouts);
     HeapSupplementable<ExecutionContext>::trace(visitor);
 #endif
     LifecycleContext<ExecutionContext>::trace(visitor);
 }
 
 } // namespace blink