bug 1215657 - make AccessibleWrap::accDoDefaultAction work with proxies r=davidb

accessible/windows/msaa/AccessibleWrap.cpp

@@ -1134,7 +1134,7 @@ AccessibleWrap::accDoDefaultAction(
 
   // TODO make this work with proxies.
   if (xpAccessible->IsProxy())
-    return E_NOTIMPL;
+    return xpAccessible->Proxy()->DoAction(0) ? S_OK : E_INVALIDARG;
 
   return xpAccessible->DoAction(0) ? S_OK : E_INVALIDARG;