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

Source/core/dom/ActiveDOMObject.h

 /*
  * 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 37 matching lines @@
     // this object must not be garbage collected.
     //
     // Default implementation is that it returns true iff
     // m_pendingActivityCount is non-zero.
     virtual bool hasPendingActivity() const;
 
     // These methods have an empty default implementation so that subclasses
     // which don't need special treatment can skip implementation.
     virtual void suspend();
     virtual void resume();
-    // willStop is called when stop() for the owner worker is called. It's not
-    // called if the owner is a Document. It's ok to post a task to the context.
-    virtual void willStop();
     virtual void stop();
 
     void didMoveToNewExecutionContext(ExecutionContext*);
 
 protected:
     virtual ~ActiveDOMObject();
 
     template<class T> void setPendingActivity(T* thisObject)
     {
         ASSERT(thisObject == this);
@@ skipping 11 matching lines @@
 private:
     unsigned m_pendingActivityCount;
 #if !ASSERT_DISABLED
     bool m_suspendIfNeededCalled;
 #endif
 };
 
 } // namespace WebCore
 
 #endif // ActiveDOMObject_h