Add CHECKs in WindowProxy initialization/detach to enforce invariants

third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp

 /*
  * Copyright (C) 2008, 2009, 2011 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 74 matching lines @@
   // clearForNavigation().
   DLOG_IF(FATAL, m_isGlobalObjectAttached)
       << "Context not detached by calling clearForNavigation()";
 
   v8::Local<v8::Object> global = m_globalProxy.newLocal(m_isolate);
   m_globalProxy.clear();
   return global;
 }
 
 void WindowProxy::setGlobal(v8::Local<v8::Object> global) {
+  CHECK(m_globalProxy.isEmpty());
   m_globalProxy.set(m_isolate, global);
 
   // Initialize the window proxy now, to re-establish the connection between
   // the global object and the v8::Context. This is really only needed for a
   // RemoteDOMWindow, since it has no scripting environment of its own.
   // Without this, existing script references to a swapped in RemoteDOMWindow
   // would be broken until that RemoteDOMWindow was vended again through an
   // interface like window.frames.
   initializeIfNeeded();
 }
@@ skipping 35 matching lines @@
 // it won't be able to reach the outer window via its global object.
 void WindowProxy::initializeIfNeeded() {
   // TODO(haraken): It is wrong to re-initialize an already detached window
   // proxy. This must be 'if(m_lifecycle == Lifecycle::ContextUninitialized)'.
   if (m_lifecycle != Lifecycle::ContextInitialized) {
     initialize();
   }
 }
 
 }  // namespace blink