Bug 1443429 - P4. Ensure MediaShutdownManager is initialized outside stable state. r=pehrsons

Differential Revision: https://phabricator.services.mozilla.com/D14283

dom/html/HTMLMediaElement.cpp

@@ -35,6 +35,7 @@
 #include "MediaManager.h"
 #include "MediaMetadataManager.h"
 #include "MediaResource.h"
+#include "MediaShutdownManager.h"
 #include "MediaSourceDecoder.h"
 #include "MediaStreamError.h"
 #include "MediaStreamGraph.h"
@@ -3452,6 +3453,12 @@ HTMLMediaElement::HTMLMediaElement(
   RegisterActivityObserver();
   NotifyOwnerDocumentActivityChanged();
 
+  // We initialize the MediaShutdownManager as the HTMLMediaElement is always
+  // constructed on the main thread, and not during stable state.
+  // (MediaShutdownManager make use of nsIAsyncShutdownClient which is written
+  // in JS)
+  MediaShutdownManager::InitStatics();
+
   mShutdownObserver->Subscribe(this);
 }