Correctly reference global proxy in the partial snapshot.

src/factory.h

Index: src/factory.h
diff --git a/src/factory.h b/src/factory.h
index 1cf5dbaf856b5c6460ef3aaac8766ce6911e3657..141fc5e66e8279c9d9d7ed48e6bdb5c009776a2f 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -465,6 +465,8 @@ class Factory FINAL {
   void ReinitializeJSGlobalProxy(Handle<JSGlobalProxy> global,
                                  Handle<JSFunction> constructor);
 
+  Handle<JSGlobalProxy> NewUninitializedJSGlobalProxy();
+
   // Change the type of the argument into a JS object/function and reinitialize.
   void BecomeJSObject(Handle<JSProxy> object);
   void BecomeJSFunction(Handle<JSProxy> object);