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

Source/web/FrameLoaderClientImpl.cpp

Index: Source/web/FrameLoaderClientImpl.cpp
diff --git a/Source/web/FrameLoaderClientImpl.cpp b/Source/web/FrameLoaderClientImpl.cpp
index c8cb57f3fdceacbd6aa7637ef22b3a88ed6ea581..ded6730b5a508b7a237f1870ad1863f74af7702f 100644
--- a/Source/web/FrameLoaderClientImpl.cpp
+++ b/Source/web/FrameLoaderClientImpl.cpp
@@ -111,10 +111,10 @@ FrameLoaderClientImpl::~FrameLoaderClientImpl()
 {
 }
 
-void FrameLoaderClientImpl::dispatchDidClearWindowObjectInWorld(DOMWrapperWorld* world)
+void FrameLoaderClientImpl::dispatchDidClearWindowObjectInWorld(DOMWrapperWorld& world)
 {
     if (m_webFrame->client()) {
-        m_webFrame->client()->didClearWindowObject(m_webFrame, world->worldId());
+        m_webFrame->client()->didClearWindowObject(m_webFrame, world.worldId());
         Document* document = m_webFrame->frame()->document();
         if (document) {
             WheelController::from(*document);