[Media, Video] Enable the video track for a new renderer.

media/blink/webmediaplayer_impl.h

Index: media/blink/webmediaplayer_impl.h
diff --git a/media/blink/webmediaplayer_impl.h b/media/blink/webmediaplayer_impl.h
index 54021e6496e7ae93dbdc103fb91cdd3b74747909..225bc0adac125f15a3ba3df01d6d46d4240e7f9a 100644
--- a/media/blink/webmediaplayer_impl.h
+++ b/media/blink/webmediaplayer_impl.h
@@ -251,6 +251,8 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
   void DisableOverlay();
 
   void OnPipelineSuspended();
+  void OnBeforePipelineResume();
+  void OnPipelineResumed();
   void OnDemuxerOpened();
 
   // Pipeline::Client overrides.
@@ -374,6 +376,22 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
   // Whether the media should be paused when hidden.
   bool ShouldPauseWhenHidden() const;
 
+  // Whether the video track should be disabled when hidden.
+  bool ShouldDisableVideoWhenHidden() const;
+
+  // Disables the video track to save power if possible.
+  // Must be called when the video was hidden and also when pipeline seeked or
+  // resumed if the video is hidden.
+  void DisableVideoTrackIfNeeded();
+
+  // Enables the video track if it was disabled before to save power,
+  // if possible.
+  // Must be called when the video was shown and also when pipeline seeked or
+  // resumed if the video is shown.
+  // Must also be called when the pipeline is about to resume, see
+  // https://crbug.com/678374.

[sandersd (OOO until July 31), 2017/01/10 21:34:37]

Somewhat confusing, in particular because resume is listed twice.

It's also not true that (as I understand it) to add the track back for a seek;
only for start (but please comment that |seeking_| is used as a proxy for
starting).

It's probably true that we don't want to change the active tracks during a seek,
so I won't recommend changing to testing for 'starting' explicitly. (But if you
do want it to be more explicit, you can rename and set |is_pipeline_resuming_|
during startup.)

[whywhat, 2017/01/11 19:41:30]

Rephrased the comments, hopefully they are less confusing now.

+  void EnableVideoTrackIfNeeded();
+
   blink::WebLocalFrame* frame_;
 
   // The playback state last reported to |delegate_|, to avoid setting duplicate
@@ -602,6 +620,12 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
   // Whether the player is currently in autoplay muted state.
   bool autoplay_muted_ = false;
 
+  // Whether disabled the video track as an optimization.
+  bool video_track_disabled_ = false;
+
+  // Whether the pipeline is being resumed at the moment.
+  bool is_pipeline_resuming_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(WebMediaPlayerImpl);
 };