Bug 1298027 - Relax decoder shutdown and mediakey removal on MediaElement suspension. r=cpearce

This changeset relaxes the shutting down of decoders and removal of mediakeys
when suspending HTMLMediaElements. This should now only happen for adobe
primetime. This alleviates, for non-primetime CDMs, the issue of videos
breaking when moving an EME protected video from a tab to a new window.

These conditions can be relaxed as neither clearkey or widevine support
secure stop. This means we don't need to shutdown their decoders and keys to
signal a stoppage, as at this stage, doing so doesn't give us secure stop and
instead means that playback is busted when we try to resume.

MozReview-Commit-ID: 3MGNXGGDVLS

--HG--
extra : rebase_source : a13fd5fa570a6868af6c3ed7b3dbfab173a9ffef

dom/html/HTMLMediaElement.cpp

@@ -12,6 +12,7 @@
 #include "mozilla/MathAlgorithms.h"
 #include "mozilla/AsyncEventDispatcher.h"
 #include "mozilla/dom/MediaEncryptedEvent.h"
+#include "mozilla/EMEUtils.h"
 
 #include "base/basictypes.h"
 #include "nsIDOMHTMLMediaElement.h"
@@ -5249,16 +5250,23 @@ void HTMLMediaElement::SuspendOrResumeElement(bool aPauseElement, bool aSuspendE
       ReportTelemetry();
       ReportEMETelemetry();
 
-      // For EME content, force destruction of the CDM client (and CDM
+      // For EME content, we may force destruction of the CDM client (and CDM
       // instance if this is the last client for that CDM instance) and
       // the CDM's decoder. This ensures the CDM gets reliable and prompt
       // shutdown notifications, as it may have book-keeping it needs
       // to do on shutdown.
       if (mMediaKeys) {
-        mMediaKeys->Shutdown();
-        mMediaKeys = nullptr;
-        if (mDecoder) {
-          ShutdownDecoder();
+        nsAutoString keySystem;
+        mMediaKeys->GetKeySystem(keySystem);
+        // If we're using Primetime we need to shutdown the key system and
+        // decoder to preserve secure stop like behavior, other CDMs don't
+        // implement this so we don't need to worry with them.
+        if (IsPrimetimeKeySystem(keySystem)) {
+          mMediaKeys->Shutdown();
+          mMediaKeys = nullptr;
+          if (mDecoder) {
+            ShutdownDecoder();
+          }
         }
       }
       if (mDecoder) {
@@ -5267,7 +5275,6 @@ void HTMLMediaElement::SuspendOrResumeElement(bool aPauseElement, bool aSuspendE
       }
       mEventDeliveryPaused = aSuspendEvents;
     } else {
-      MOZ_ASSERT(!mMediaKeys);
       if (mDecoder) {
         mDecoder->Resume();
         if (!mPaused && !mDecoder->IsEnded()) {