Bug 1278443 - Part 2: Continue to run the worker even if BackgroundChild fails to create. r=mrbkap

MozReview-Commit-ID: LBBN4hfXigf

--HG--
extra : rebase_source : f35e75eebf051ec5eb6948bbeb7742a573168602

dom/workers/RuntimeService.cpp

@@ -2808,7 +2808,8 @@ WorkerThreadPrimaryRunnable::Run()
   //       worker messages here.
   if (NS_WARN_IF(!BackgroundChild::SynchronouslyCreateForCurrentThread())) {
     // XXX need to fire an error at parent.
-    return NS_ERROR_UNEXPECTED;
+    // Failed in creating BackgroundChild: probably in shutdown. Continue to run
+    // without BackgroundChild created.
   }
 
   class MOZ_STACK_CLASS SetThreadHelper final