Make DOMWrapperWorlds easier to use

Source/bindings/v8/DOMWrapperWorld.h

Index: Source/bindings/v8/DOMWrapperWorld.h
diff --git a/Source/bindings/v8/DOMWrapperWorld.h b/Source/bindings/v8/DOMWrapperWorld.h
index f181efce51e3ac71f0527021207495cab885fc17..d503bc8e3a983276e1c50edaccf7033059c54675 100644
--- a/Source/bindings/v8/DOMWrapperWorld.h
+++ b/Source/bindings/v8/DOMWrapperWorld.h
@@ -43,6 +43,7 @@
 namespace WebCore {
 
 class DOMDataStore;
+class ScriptExecutionContext;
 
 // This class represent a collection of DOM wrappers for a specific world.
 class DOMWrapperWorld : public RefCounted<DOMWrapperWorld> {
@@ -65,6 +66,9 @@ public:
         return static_cast<DOMWrapperWorld*>(context->GetAlignedPointerFromEmbedderData(v8ContextIsolatedWorld));
     }
 
+    // Will return null if there is no DOMWrapperWorld representing the given ScriptExecutionContext.
+    static DOMWrapperWorld* current(ScriptExecutionContext*);
+
     // 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.