Accessing the returnValue of a modal dialog should be performed directly on the globa...

Accessing the returnValue of a modal dialog should be performed directly on the global object.
https://bugs.webkit.org/show_bug.cgi?id=83414

Reviewed by Gavin Barraclough.

Presumably during the mass-devirtualising of JSObject, this deliberate use of
the GlobalObject's property lookup logic directly was replaced with a dynamic
call.  That results in the DOMWindow filtering out the lookup.  This regression
was masked by r93567.

* bindings/js/JSDOMWindowCustom.cpp:
(WebCore::DialogHandler::returnValue):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@113528 268f45cc-cd09-0410-ab3c-d52691b4dbfc