Bug 1872787 change non-fatal MediaTrackGraph shutdown assertion to MOZ_DIAGNOSTIC_ASSERT r=padenot

If the graph leaks because it does not shut down its driver, then an nsThread
can be leaked and block shutdown at nsThreadManager::ShutdownNonMainThreads().
The shutdown blocker has better debug messages to identify the source of the
blockage than ShutdownNonMainThreads(), so I'd like to remove
MediaTrackGraph's code that removes it's shutdown blocker after a timeout.
This new assert is intended to give some visibility into how many problems
such removal might cause.

Depends on D198769

Differential Revision: https://phabricator.services.mozilla.com/D198770

dom/media/MediaTrackGraph.cpp

@@ -1712,8 +1712,8 @@ void MediaTrackGraphImpl::ForceShutDown() {
 NS_IMETHODIMP
 MediaTrackGraphImpl::Notify(nsITimer* aTimer) {
   MOZ_ASSERT(NS_IsMainThread());
-  NS_ASSERTION(!mShutdownBlocker,
-               "MediaTrackGraph took too long to shut down!");
+  MOZ_DIAGNOSTIC_ASSERT(!mShutdownBlocker,
+                        "MediaTrackGraph took too long to shut down!");
   // Sigh, graph took too long to shut down.  Stop blocking system
   // shutdown and hope all is well.
   RemoveShutdownBlocker();