Bug 1786306 assert that there is no more than one output for each key on a track r=padenot

SetAudioOutputVolume() assumes this.

Depends on D158304

Differential Revision: https://phabricator.services.mozilla.com/D158305

dom/media/MediaTrackGraph.cpp

@@ -825,6 +825,7 @@ void MediaTrackGraphImpl::CloseAudioInputImpl(DeviceInputTrack* aTrack) {
 
 void MediaTrackGraphImpl::RegisterAudioOutput(MediaTrack* aTrack, void* aKey) {
   MOZ_ASSERT(OnGraphThread());
+  MOZ_ASSERT(!mAudioOutputs.Contains(TrackAndKey{aTrack, aKey}));
 
   TrackKeyAndVolume* tkv = mAudioOutputs.AppendElement();
   tkv->mTrack = aTrack;
@@ -861,10 +862,7 @@ void MediaTrackGraphImpl::UnregisterAudioOutput(MediaTrack* aTrack,
                                                 void* aKey) {
   MOZ_ASSERT(OnGraphThreadOrNotRunning());
 
-  mAudioOutputs.RemoveElementsBy(
-      [&aKey, &aTrack](const TrackKeyAndVolume& aTkv) {
-        return aTkv.mKey == aKey && aTkv.mTrack == aTrack;
-      });
+  mAudioOutputs.RemoveElement(TrackAndKey{aTrack, aKey});
 }
 
 void MediaTrackGraphImpl::CloseAudioInput(DeviceInputTrack* aTrack) {

dom/media/MediaTrackGraphImpl.h

@@ -414,6 +414,10 @@ class MediaTrackGraphImpl : public MediaTrackGraph,
    * Queue audio (mix of track audio and silence for blocked intervals)
    * to the audio output track. Returns the number of frames played.
    */
+  struct TrackAndKey {
+    MediaTrack* mTrack;
+    void* mKey;
+  };
   struct TrackKeyAndVolume {
     MediaTrack* mTrack;
     void* mKey;
@@ -1046,4 +1050,16 @@ class MediaTrackGraphImpl : public MediaTrackGraph,
 
 }  // namespace mozilla
 
+template <>
+class nsDefaultComparator<mozilla::MediaTrackGraphImpl::TrackKeyAndVolume,
+                          mozilla::MediaTrackGraphImpl::TrackAndKey> {
+ public:
+  bool Equals(
+      const mozilla::MediaTrackGraphImpl::TrackKeyAndVolume& aElement,
+      const mozilla::MediaTrackGraphImpl::TrackAndKey& aTrackAndKey) const {
+    return aElement.mTrack == aTrackAndKey.mTrack &&
+           aElement.mKey == aTrackAndKey.mKey;
+  }
+};
+
 #endif /* MEDIATRACKGRAPHIMPL_H_ */