Revert of Make DOMWrapperWorld::current() return a reference instead of a pointer

Source/bindings/v8/DOMWrapperWorld.h

 /*
  * Copyright (C) 2009 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 51 matching lines @@
     static PassRefPtr<DOMWrapperWorld> create(int worldId = -1, int extensionGroup = -1);
 
     static const int mainWorldExtensionGroup = 0;
     static PassRefPtr<DOMWrapperWorld> ensureIsolatedWorld(int worldId, int extensionGroup);
     ~DOMWrapperWorld();
     void dispose();
 
     static bool isolatedWorldsExist() { return isolatedWorldCount; }
     static void allWorldsInMainThread(Vector<RefPtr<DOMWrapperWorld> >& worlds);
 
-    static DOMWrapperWorld& world(v8::Handle<v8::Context> context)
+    static DOMWrapperWorld* world(v8::Handle<v8::Context> context)
     {
         ASSERT(!context.IsEmpty());
         return V8PerContextData::world(context);
     }
 
-    static DOMWrapperWorld& current(v8::Isolate* isolate)
+    // Will return null if there is no DOMWrapperWorld for the current context.
+    static DOMWrapperWorld* current(v8::Isolate* isolate)
     {
         if (isMainThread() && worldOfInitializingWindow) {
             // It's possible that current() is being called while window is being initialized.
             // In order to make current() workable during the initialization phase,
             // we cache the world of the initializing window on worldOfInitializingWindow.
             // If there is no initiazing window, worldOfInitializingWindow is 0.
-            return *worldOfInitializingWindow;
+            return worldOfInitializingWindow;
         }
         return world(isolate->GetCurrentContext());
     }
 
-    static DOMWrapperWorld& mainWorld();
+    static DOMWrapperWorld* mainWorld();
 
     // Associates an isolated world (see above for description) with a security
     // origin. XMLHttpRequest instances used in that world will be considered
     // to come from that origin, not the frame's.
     static void setIsolatedWorldSecurityOrigin(int worldID, PassRefPtr<SecurityOrigin>);
     static void clearIsolatedWorldSecurityOrigin(int worldID);
     SecurityOrigin* isolatedWorldSecurityOrigin();
 
     // Associated an isolated world with a Content Security Policy. Resources
     // embedded into the main world's DOM from script executed in an isolated
@@ skipping 30 matching lines @@
     static DOMWrapperWorld* worldOfInitializingWindow;
 
     const int m_worldId;
     const int m_extensionGroup;
     OwnPtr<DOMDataStore> m_domDataStore;
 };
 
 } // namespace WebCore
 
 #endif // DOMWrapperWorld_h