Bug 1503132 initialize mEndTime to zero for offline graphs r=padenot

This will prevent rendering from starting when the graph thread is started
before StartNonRealtimeProcessing() is called.

Depends on D10167

Differential Revision: https://phabricator.services.mozilla.com/D10168

--HG--
extra : moz-landing-system : lando

dom/media/MediaStreamGraph.cpp

@@ -3680,7 +3680,8 @@ MediaStreamGraphImpl::MediaStreamGraphImpl(GraphDriverType aDriverRequested,
   , mGraphDriverAsleep(false)
   , mMonitor("MediaStreamGraphImpl")
   , mLifecycleState(LIFECYCLE_THREAD_NOT_STARTED)
-  , mEndTime(GRAPH_TIME_MAX)
+  // An offline graph is not initially processing.
+  , mEndTime(aDriverRequested == OFFLINE_THREAD_DRIVER ? 0 : GRAPH_TIME_MAX)
   , mForceShutDown(false)
   , mPostedRunInStableStateEvent(false)
   , mDetectedNotRunning(false)