AtomicString usage improvements in v8 interceptors.

third_party/WebKit/WebCore/bindings/v8/custom/V8DOMWindowCustom.cpp

Index: third_party/WebKit/WebCore/bindings/v8/custom/V8DOMWindowCustom.cpp
===================================================================
--- third_party/WebKit/WebCore/bindings/v8/custom/V8DOMWindowCustom.cpp	(revision 13552)
+++ third_party/WebKit/WebCore/bindings/v8/custom/V8DOMWindowCustom.cpp	(working copy)
@@ -536,13 +536,13 @@
     if (!window)
         return notHandledByInterceptor();
 
-    String propName = toWebCoreString(name);
-
     Frame* frame = window->frame();
     // window is detached from a frame.
     if (!frame)
         return notHandledByInterceptor();
 
+    AtomicString propName = v8StringToAtomicWebCoreString(name);
+
     // Search sub-frames.
     Frame* child = frame->tree()->child(propName);
     if (child)