Video Capture: Allow suspension of individual devices.

media/base/video_capturer_source.h

Index: media/base/video_capturer_source.h
diff --git a/media/base/video_capturer_source.h b/media/base/video_capturer_source.h
index ddec90c6599b26b564984e0b347d22472b4ca0df..edda400475ec26f01f8311dbef6427b7cb0d26a0 100644
--- a/media/base/video_capturer_source.h
+++ b/media/base/video_capturer_source.h
@@ -86,6 +86,14 @@ class MEDIA_EXPORT VideoCapturerSource {
   // successfully, then |new_frame_callback| should be called with a frame.
   virtual void RequestRefreshFrame() {}
 
+  // Optionally suspends frame delivery. The source may or may not honor this
+  // request. The purpose of this is to allow minimizing resource usage while
+  // there are no frame consumers present.
+  virtual void MaybeSuspend() {}

[xhwang, 2016/09/28 21:09:56]

nit: How will the caller know whether it can/should call Resume() if it doesn't
know whether "suspend" request is honored?

[miu, 2016/09/28 21:52:14]

Added explanation in comments.

+
+  // Resumes frame delivery, if it was suspended.

[xhwang, 2016/09/28 21:09:56]

nit: What if "it was not suspended"? Will it fail, no-op, or DCHECK? What if
capturing never "started"?

[miu, 2016/09/28 21:52:14]

Added explanation in comments for this too.

+  virtual void Resume() {}
+
   // Stops capturing frames and clears all callbacks including the
   // SupportedFormatsCallback callback. Note that queued frame callbacks
   // may still occur after this call, so the caller must take care to