Bug 1539045 remove unnecessary !mRealtime checks with mForcedShutDown r=padenot

These are unnecessary because non-empty !mRealtime graphs also set
mForcedShutDown before progressing to
LIFECYCLE_WAITING_FOR_MAIN_THREAD_CLEANUP.

This reverts some of
https://hg.mozilla.org/mozilla-central/rev/d0d427badc22afa7d5406e4e376bf27df0c0aaba#l1.72
which is possible because a non-realtime graph no longer progresses to
LIFECYCLE_WAITING_FOR_MAIN_THREAD_CLEANUP when it reaches mEndTime since
https://hg.mozilla.org/mozilla-central/rev/61d08765489c#l1.41

Differential Revision: https://phabricator.services.mozilla.com/D24855

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

dom/media/MediaStreamGraph.cpp

@@ -1558,12 +1558,11 @@ class MediaStreamGraphShutDownRunnable : public Runnable {
       // mGraph is no longer needed, so delete it.
       mGraph->Destroy();
     } else {
-      // The graph is not empty.  We must be in a forced shutdown, or a
-      // non-realtime graph that has finished processing. Some later
-      // AppendMessage will detect that the graph has been emptied, and
-      // delete it.
-      NS_ASSERTION(mGraph->mForceShutDown || !mGraph->mRealtime,
-                   "Not in forced shutdown?");
+      // The graph is not empty.  We must be in a forced shutdown, either for
+      // process shutdown or a non-realtime graph that has finished
+      // processing. Some later AppendMessage will detect that the graph has
+      // been emptied, and delete it.
+      NS_ASSERTION(mGraph->mForceShutDown, "Not in forced shutdown?");
       mGraph->LifecycleStateRef() =
           MediaStreamGraphImpl::LIFECYCLE_WAITING_FOR_STREAM_DESTRUCTION;
     }
@@ -1730,7 +1729,7 @@ void MediaStreamGraphImpl::RunInStableState(bool aSourceIsMSG) {
       }
     }
 
-    if ((mForceShutDown || !mRealtime) &&
+    if (mForceShutDown &&
         LifecycleStateRef() == LIFECYCLE_WAITING_FOR_MAIN_THREAD_CLEANUP) {
       // Defer calls to RunDuringShutdown() to happen while mMonitor is not
       // held.

dom/media/MediaStreamGraphImpl.h

@@ -812,7 +812,8 @@ class MediaStreamGraphImpl : public MediaStreamGraph,
   }
 
   /**
-   * True when we need to do a forced shutdown during application shutdown.
+   * True when we need to do a forced shutdown, during application shutdown or
+   * when shutting down a non-realtime graph.
    * Only set on main thread.
    * Can be read safely on the main thread, on all other threads mMonitor must
    * be held.