Bug 854924 - Change "can't allocate graphics resources" in TabParent to an NS_WARNING. r=bent

We hit this assertion during our tests, which sometimes complete before
the subprocess is Show()'n.  This isn't a bug, as far as I can tell.

Changing the NS_ERROR to NS_WARNING keeps us from failing on tryserver.

--HG--
extra : rebase_source : fe98bcd891f9255297240c96b65ae39fe6112bd3

dom/ipc/TabParent.cpp

@@ -1275,7 +1275,7 @@ TabParent::AllocPRenderFrame(ScrollingBehavior* aScrolling,
 
   nsRefPtr<nsFrameLoader> frameLoader = GetFrameLoader();
   if (!frameLoader) {
-    NS_ERROR("Can't allocate graphics resources, aborting subprocess");
+    NS_WARNING("Can't allocate graphics resources, aborting subprocess");
     return nullptr;
   }