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

Source/bindings/v8/V8Binding.h

Index: Source/bindings/v8/V8Binding.h
diff --git a/Source/bindings/v8/V8Binding.h b/Source/bindings/v8/V8Binding.h
index 5afa6cd4585ee0810abeb12cc4d02e95f288a3a8..dc33490b34162f59ab59ab5a369c535ac456235e 100644
--- a/Source/bindings/v8/V8Binding.h
+++ b/Source/bindings/v8/V8Binding.h
@@ -657,10 +657,10 @@ ExecutionContext* callingExecutionContext(v8::Isolate*);
 
 // Returns a V8 context associated with a ExecutionContext and a DOMWrapperWorld.
 // This method returns an empty context if there is no frame or the frame is already detached.
-v8::Local<v8::Context> toV8Context(ExecutionContext*, DOMWrapperWorld&);
+v8::Local<v8::Context> toV8Context(ExecutionContext*, DOMWrapperWorld*);
 // Returns a V8 context associated with a LocalFrame and a DOMWrapperWorld.
 // This method returns an empty context if the frame is already detached.
-v8::Local<v8::Context> toV8Context(v8::Isolate*, LocalFrame*, DOMWrapperWorld&);
+v8::Local<v8::Context> toV8Context(v8::Isolate*, LocalFrame*, DOMWrapperWorld*);
 
 // Returns the frame object of the window object associated with
 // a context, if the window is currently being displayed in the LocalFrame.