Request frame for new sinks from MediaStreamVideoTrack

media/base/video_capturer_source.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_BASE_VIDEO_CAPTURER_SOURCE_H_
 #define MEDIA_BASE_VIDEO_CAPTURER_SOURCE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 58 matching lines @@
   // argument) if called with the wrong task runner.
   // If capturing fails to start or stopped due to an external event then
   // |running_callback| will be called with a parameter of false.
   // |running_callback| will always be called on the same thread as the
   // StartCapture.
   virtual void StartCapture(
       const media::VideoCaptureParams& params,
       const VideoCaptureDeliverFrameCB& new_frame_callback,
       const RunningCallback& running_callback) = 0;
 
+  // Asks source to send a refresh frame. In cases where source does not provide
+  // a continuous rate of new frames (e.g. canvas capture, screen capture where
+  // the screen's content has not changed in a while), consumers may request a
+  // "refresh frame" to be delivered. For instance, this would be needed when
+  // a new sink is added to a MediaStreamTrack.
+  // The default implementation is a no-op and implementations are not required
+  // to honor this request. If they decide to and capturing is started
+  // successfully, then |new_frame_callback| should be called with a frame.
+  virtual void RequestRefreshFrame() {}
+
   // 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
   // use refcounted or weak references in |new_frame_callback|.
   virtual void StopCapture() = 0;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_CAPTURER_SOURCE_H_