bug 1406831 tighten AssertOnGraphThreadOrNotRunning() to not accept graph thread after mDetectedNotRunning r=pehrsons

This also permits setting mDriver to null after mDetectedNotRunning, which is
useful for fixing bug 1406830.

MozReview-Commit-ID: EEgAxqPQPRI

--HG--
extra : rebase_source : 56e1583a0090e683e92463536637d0f1460cb727

dom/media/MediaStreamGraph.cpp

@@ -1124,11 +1124,10 @@ MediaStreamGraph::AssertOnGraphThreadOrNotRunning() const
   MediaStreamGraphImpl const * graph =
     static_cast<MediaStreamGraphImpl const *>(this);
   // if all the safety checks fail, assert we own the monitor
-  if (!graph->mDriver->OnThread()) {
-    if (!(graph->mDetectedNotRunning &&
-          NS_IsMainThread())) {
+  if (!(graph->mDetectedNotRunning ?
+        NS_IsMainThread() : graph->mDriver->OnThread()))
+  {
       graph->mMonitor.AssertCurrentThreadOwns();
-    }
   }
 #endif
 }