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

Source/core/loader/FrameLoader.cpp

Index: Source/core/loader/FrameLoader.cpp
diff --git a/Source/core/loader/FrameLoader.cpp b/Source/core/loader/FrameLoader.cpp
index 20c00570ebc7addae341661781e22fc6813983d1..139d0e777f6ad93bb11330b7f34e9b097b290516 100644
--- a/Source/core/loader/FrameLoader.cpp
+++ b/Source/core/loader/FrameLoader.cpp
@@ -1447,10 +1447,10 @@ void FrameLoader::dispatchDidClearWindowObjectsInAllWorlds()
     Vector<RefPtr<DOMWrapperWorld> > worlds;
     DOMWrapperWorld::allWorldsInMainThread(worlds);
     for (size_t i = 0; i < worlds.size(); ++i)
-        m_client->dispatchDidClearWindowObjectInWorld(worlds[i].get());
+        m_client->dispatchDidClearWindowObjectInWorld(*worlds[i]);
 }
 
-void FrameLoader::dispatchDidClearWindowObjectInWorld(DOMWrapperWorld* world)
+void FrameLoader::dispatchDidClearWindowObjectInWorld(DOMWrapperWorld& world)
 {
     if (!m_frame->script().canExecuteScripts(NotAboutToExecuteScript) || !m_frame->script().existingWindowShell(world))
         return;