Simplify and weaken DOMWindowProperty unregistration

Source/core/frame/DOMWindowProperty.cpp

 /*
  * Copyright (C) 2011 Google, Inc. All Rights Reserved.
  * Copyright (C) 2012 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
@@ skipping 32 matching lines @@
         m_associatedDOMWindow = m_frame->domWindow();
         m_associatedDOMWindow->registerProperty(this);
     }
 }
 
 #if !ENABLE(OILPAN)
 DOMWindowProperty::~DOMWindowProperty()
 {
     if (m_associatedDOMWindow)
         m_associatedDOMWindow->unregisterProperty(this);
-
-    m_associatedDOMWindow = nullptr;
-    m_frame = nullptr;
 }
 #endif
 
 void DOMWindowProperty::willDestroyGlobalObjectInFrame()
 {
     // If the property is getting this callback it must have been created with a LocalFrame/LocalDOMWindow and it should still have them.
     ASSERT(m_frame);
     ASSERT(m_associatedDOMWindow);
 
-    // DOMWindowProperty lifetime isn't tied directly to the LocalDOMWindow itself so it is important that it unregister
-    // itself from any LocalDOMWindow it is associated with if that LocalDOMWindow is going away.
-    if (m_associatedDOMWindow)
-        m_associatedDOMWindow->unregisterProperty(this);
+    // LocalDOMWindow will along with notifying DOMWindowProperty objects of
+    // impending destruction, unilaterally clear out its registered set.
+    // Consequently, no explicit unregisteration required by DOMWindowProperty;
+    // here or when finalized.
     m_associatedDOMWindow = nullptr;
     m_frame = nullptr;
 }
 
 void DOMWindowProperty::willDetachGlobalObjectFromFrame()
 {
     // If the property is getting this callback it must have been created with a LocalFrame/LocalDOMWindow and it should still have them.
     ASSERT(m_frame);
     ASSERT(m_associatedDOMWindow);
 }
 
 void DOMWindowProperty::trace(Visitor* visitor)
 {
     visitor->trace(m_associatedDOMWindow);
 }
 
 }