Remove ActiveDOMObject::willStop, and introduce WorkerGlobalScope::TerminationObserver.

Source/core/dom/ActiveDOMObject.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 61 matching lines @@
 }
 
 void ActiveDOMObject::suspend()
 {
 }
 
 void ActiveDOMObject::resume()
 {
 }
 
-void ActiveDOMObject::willStop()
-{
-}
-
 void ActiveDOMObject::stop()
 {
 }
 
 void ActiveDOMObject::didMoveToNewExecutionContext(ExecutionContext* context)
 {
     observeContext(context);
 
     if (context->activeDOMObjectsAreStopped()) {
         stop();
         return;
     }
 
     if (context->activeDOMObjectsAreSuspended()) {
         suspend();
         return;
     }
 
     resume();
 }
 
 } // namespace WebCore