Video Capture: Allow suspension of individual devices.

content/renderer/media/media_stream_video_source.h

Index: content/renderer/media/media_stream_video_source.h
diff --git a/content/renderer/media/media_stream_video_source.h b/content/renderer/media/media_stream_video_source.h
index 3d79aeafb776d0fe9c84c08615d4f688df848e34..fe2612a5359364c6a3a7f4f10b7b287ec8744b6f 100644
--- a/content/renderer/media/media_stream_video_source.h
+++ b/content/renderer/media/media_stream_video_source.h
@@ -71,14 +71,15 @@ class CONTENT_EXPORT MediaStreamVideoSource
                 const ConstraintsCallback& callback);
   void RemoveTrack(MediaStreamVideoTrack* track);
 
+  // Called by |track| to notify the source whether it has any paths to a
+  // consuming endpoint.
+  void UpdateHasConsumers(MediaStreamVideoTrack* track, bool has_consumers);
+
   void UpdateCapturingLinkSecure(MediaStreamVideoTrack* track, bool is_secure);
 
   // Request underlying source to capture a new frame.
   virtual void RequestRefreshFrame() {}
 
-  // Notify underlying source if the capturing link is secure.
-  virtual void SetCapturingLinkSecured(bool is_secure) {}
-
   // Returns the task runner where video frames will be delivered on.
   base::SingleThreadTaskRunner* io_task_runner() const;
 
@@ -126,6 +127,16 @@ class CONTENT_EXPORT MediaStreamVideoSource
   // method has been called, MediaStreamVideoSource may be deleted.
   virtual void StopSourceImpl() = 0;
 
+  // Optionally overridden by subclasses to act on whether there are any
+  // consumers present. When none are present, the source can stop delivering
+  // frames, giving it the option of running in an "idle" state to minimize
+  // resource usage.
+  virtual void OnHasConsumers(bool has_consumers) {}
+
+  // Optionally overridden by subclasses to act on whether the capturing link
+  // has become secure or insecure.
+  virtual void OnCapturingLinkSecured(bool is_secure) {}
+
   enum State {
     NEW,
     RETRIEVING_CAPABILITIES,
@@ -183,6 +194,10 @@ class CONTENT_EXPORT MediaStreamVideoSource
   // Tracks that currently are connected to this source.
   std::vector<MediaStreamVideoTrack*> tracks_;
 
+  // Tracks that have no paths to a consuming endpoint, and so do not need
+  // frames delivered from the source.

[mcasas, 2016/09/28 21:34:44]

nit: I'd add that |suspended_tracks_| is a subset of |tracks_|,
otherwise a developer might doubt if tracks are moved
between those two vectors or the can (partially) overlap.

[miu, 2016/09/28 22:35:15]

Done.

+  std::vector<MediaStreamVideoTrack*> suspended_tracks_;
+
   // This is used for tracking if all connected video sinks are secure.
   SecureDisplayLinkTracker<MediaStreamVideoTrack> secure_tracker_;