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

Source/bindings/v8/V8WindowShell.cpp

Index: Source/bindings/v8/V8WindowShell.cpp
diff --git a/Source/bindings/v8/V8WindowShell.cpp b/Source/bindings/v8/V8WindowShell.cpp
index 5e742fe3d89277f4a7cfa5a028a612241f46f820..61a55ecd8bdc97fda6e73ca6415963a830548f5b 100644
--- a/Source/bindings/v8/V8WindowShell.cpp
+++ b/Source/bindings/v8/V8WindowShell.cpp
@@ -78,9 +78,9 @@ static void setInjectedScriptContextDebugId(v8::Handle<v8::Context> targetContex
     V8PerContextDebugData::setContextDebugData(targetContext, "injected", debugId);
 }
 
-PassOwnPtr<V8WindowShell> V8WindowShell::create(LocalFrame* frame, DOMWrapperWorld& world, v8::Isolate* isolate)
+PassOwnPtr<V8WindowShell> V8WindowShell::create(LocalFrame* frame, PassRefPtr<DOMWrapperWorld> world, v8::Isolate* isolate)
 {
-    return adoptPtr(new V8WindowShell(frame, &world, isolate));
+    return adoptPtr(new V8WindowShell(frame, world, isolate));
 }
 
 V8WindowShell::V8WindowShell(LocalFrame* frame, PassRefPtr<DOMWrapperWorld> world, v8::Isolate* isolate)