Avoid snapshotting ContextLifecycleObservers when iterating.

third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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 153 matching lines @@
 
     // TODO(alexclarke): Override timerTaskRunner() to pass in a document specific default task runner.
 
 private:
     void fired() override
     {
         InspectorInstrumentation::AsyncTask asyncTask(m_window->document(), this);
         m_disposalAllowed = false;
         m_window->postMessageTimerFired(this);
         dispose();
+        // Oilpan optimization: unregister as an observer right away.
+        clearContext();
     }
 
     void dispose()
     {
-        // Oilpan optimization: unregister as an observer right away.
-        clearContext();
-        // Will destroy this object, now or after the next GC depending
-        // on whether Oilpan is disabled or not.
         m_window->removePostMessageTimer(this);
     }
 
     Member<MessageEvent> m_event;
     Member<LocalDOMWindow> m_window;
     RefPtr<SecurityOrigin> m_targetOrigin;
     std::unique_ptr<SourceLocation> m_location;
     RefPtr<UserGestureToken> m_userGestureToken;
     bool m_disposalAllowed;
 };
@@ skipping 1360 matching lines @@
 {
     // If the LocalDOMWindow still has a frame reference, that frame must point
     // back to this LocalDOMWindow: otherwise, it's easy to get into a situation
     // where script execution leaks between different LocalDOMWindows.
     if (m_frameObserver->frame())
         ASSERT_WITH_SECURITY_IMPLICATION(m_frameObserver->frame()->domWindow() == this);
     return m_frameObserver->frame();
 }
 
 } // namespace blink