Bug 1833266 - part3 : guard the PlayReady support with the media engi…

…ne pref. r=jolin

PlayReady can only be played through the media engine, so it doesn't
make sense to support it when the media engine is disabled.

Differential Revision: https://phabricator.services.mozilla.com/D178126

dom/media/eme/EMEUtils.cpp

@@ -70,6 +70,11 @@ bool IsPlayReadyKeySystemAndSupported(const nsAString& aKeySystem) {
   if (!StaticPrefs::media_eme_playready_enabled()) {
     return false;
   }
+  // 1=enabled encrypted and clear, 2=enabled encrytped.
+  if (StaticPrefs::media_wmf_media_engine_enabled() != 1 &&
+      StaticPrefs::media_wmf_media_engine_enabled() != 2) {
+    return false;
+  }
   return aKeySystem.EqualsLiteral(kPlayReadyKeySystemName) ||
          aKeySystem.EqualsLiteral(kPlayReadyKeySystemHardware);
 }