Bug 1346498 part 2 - implement the VideoDecodeMode mechanism in MDSM; r=jwwang

The MDSM::mVideoDecodeMode and MDSM::SetVideoDecodeMode() are merely a renaming of MDSM::mIsVisible and MDSM::VisibilityChanged().
However, the renaming explicitly reflects that MDSM provides mechanism only without participating in the policy decision.
Will reremove the MDSM::mIsVisible and MDSM::VisibilityChanged() in following patches.

MozReview-Commit-ID: JdMKQTgVCf3

--HG--
extra : rebase_source : 95977b205f235b6a456d12dfde93fe84f3b12aa7
extra : source : 4382a3c10f30653d5a70abb3bd4b8146a4272784

dom/media/MediaDecoderStateMachine.cpp

@@ -2611,6 +2611,7 @@ MediaDecoderStateMachine::MediaDecoderStateMachine(MediaDecoder* aDecoder,
   mVideoDecodeSuspendTimer(mTaskQueue),
   mOutputStreamManager(new OutputStreamManager()),
   mResource(aDecoder->GetResource()),
+  mVideoDecodeMode(VideoDecodeMode::Normal),
   mIsMSE(aDecoder->IsMSE()),
   INIT_MIRROR(mBuffered, TimeIntervals()),
   INIT_MIRROR(mEstimatedDuration, NullableTimeUnit()),
@@ -3068,6 +3069,56 @@ void MediaDecoderStateMachine::SuspendTaintChanged()
   }
 }
 
+void MediaDecoderStateMachine::SetVideoDecodeMode(VideoDecodeMode aMode)
+{
+  nsCOMPtr<nsIRunnable> r =
+    NewRunnableMethod<VideoDecodeMode>(this,
+                                       &MediaDecoderStateMachine::SetVideoDecodeModeInternal,
+                                       aMode);
+  OwnerThread()->DispatchStateChange(r.forget());
+}
+
+void MediaDecoderStateMachine::SetVideoDecodeModeInternal(VideoDecodeMode aMode)
+{
+  MOZ_ASSERT(OnTaskQueue());
+  DECODER_LOG("VideoDecodeModeChanged: VideoDecodeMode=(%s->%s), mVideoDecodeSuspended=%c",
+              mVideoDecodeMode == VideoDecodeMode::Normal ? "Normal" : "Suspend",
+              aMode == VideoDecodeMode::Normal ? "Normal" : "Suspend",
+              mVideoDecodeSuspended ? 'T' : 'F');
+
+  if (!MediaPrefs::MDSMSuspendBackgroundVideoEnabled()) {
+    return;
+  }
+
+  if (aMode == mVideoDecodeMode) {
+    return;
+  }
+
+  // Set new video decode mode.
+  mVideoDecodeMode = aMode;
+
+  // Start timer to trigger suspended video decoding.
+  if (mVideoDecodeMode == VideoDecodeMode::Suspend) {
+    TimeStamp target = TimeStamp::Now() + SuspendBackgroundVideoDelay();
+
+    RefPtr<MediaDecoderStateMachine> self = this;
+    mVideoDecodeSuspendTimer.Ensure(target,
+                                    [=]() { self->OnSuspendTimerResolved(); },
+                                    [] () { MOZ_DIAGNOSTIC_ASSERT(false); });
+    mOnPlaybackEvent.Notify(MediaEventType::StartVideoSuspendTimer);
+    return;
+  }
+
+  // Resuming from suspended decoding
+
+  // If suspend timer exists, destroy it.
+  CancelSuspendTimer();
+
+  if (mVideoDecodeSuspended) {
+    mStateObj->HandleResumeVideoDecoding();
+  }
+}
+
 void MediaDecoderStateMachine::BufferedRangeUpdated()
 {
   MOZ_ASSERT(OnTaskQueue());

dom/media/MediaDecoderStateMachine.h

@@ -127,6 +127,12 @@ enum class MediaEventType : int8_t
   CancelVideoSuspendTimer
 };
 
+enum class VideoDecodeMode : uint8_t
+{
+  Normal,
+  Suspend
+};
+
 /*
   The state machine class. This manages the decoding and seeking in the
   MediaDecoderReader on the decode task queue, and A/V sync on the shared
@@ -226,6 +232,9 @@ public:
 
   size_t SizeOfAudioQueue() const;
 
+  // Sets the video decode mode. Used by the suspend-video-decoder feature.
+  void SetVideoDecodeMode(VideoDecodeMode aMode);
+
 private:
   class StateObject;
   class DecodeMetadataState;
@@ -307,6 +316,8 @@ private:
   void ResetDecode(TrackSet aTracks = TrackSet(TrackInfo::kAudioTrack,
                                                TrackInfo::kVideoTrack));
 
+  void SetVideoDecodeModeInternal(VideoDecodeMode aMode);
+
 protected:
   virtual ~MediaDecoderStateMachine();
 
@@ -676,6 +687,9 @@ private:
   // Media data resource from the decoder.
   RefPtr<MediaResource> mResource;
 
+  // Track the current video decode mode.
+  VideoDecodeMode mVideoDecodeMode;
+
   // Track the complete & error for audio/video separately
   MozPromiseRequestHolder<GenericPromise> mMediaSinkAudioPromise;
   MozPromiseRequestHolder<GenericPromise> mMediaSinkVideoPromise;