Video Capture: Allow suspension of individual devices.

media/capture/video/video_capture_device.h

 // Copyright (c) 2012 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.
 //
 // VideoCaptureDevice is the abstract base class for realizing video capture
 // device support in Chromium. It provides the interface for OS dependent
 // implementations.
 // The class is created and functions are invoked on a thread owned by
 // VideoCaptureManager. Capturing is done on other threads, depending on the OS
 // specific implementation.
@@ skipping 149 matching lines @@
   //      improve the video quality of unchanging content.
   //
   // The default implementation is a no-op. VideoCaptureDevice implementations
   // are not required to honor this request, especially if they do not
   // self-pause and/or if honoring the request would cause them to exceed their
   // configured maximum frame rate. Any VideoCaptureDevice that does self-pause,
   // however, should provide an implementation of this method that makes
   // reasonable attempts to honor these requests.
   virtual void RequestRefreshFrame() {}
 
+  // Optionally suspends frame delivery. The VideoCaptureDevice may or may not
+  // honor this request. The purpose of this is to quickly place the device into
+  // a state where it's resource utilization is minimized while there are no
+  // frame consumers; and then quickly resume once a frame consumer is present.
+  virtual void MaybeSuspend() {}

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

Could we say here MaybePause()? It would sound
to  me as the complementary operation of 
Resume(), and sort-of like a VCR recorder. But
I'm no Merriam nor Webster so I'll agree to your view.

+
+  // Resumes frame delivery, if it was suspended.
+  virtual void Resume() {}
+
   // Deallocates the video capturer, possibly asynchronously.
   //
   // This call requires the device to do the following things, eventually: put
   // hardware into a state where other applications could use it, free the
   // memory associated with capture, and delete the |client| pointer passed into
   // AllocateAndStart.
   //
   // If deallocation is done asynchronously, then the device implementation must
   // ensure that a subsequent AllocateAndStart() operation targeting the same ID
   // would be sequenced through the same task runner, so that deallocation
@@ skipping 24 matching lines @@
 
  private:
   // Gets the power line frequency from the current system time zone if this is
   // defined, otherwise returns 0.
   PowerLineFrequency GetPowerLineFrequencyForLocation() const;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_DEVICE_H_