getUserMeida: report device starting states

content/browser/renderer_host/media/video_capture_controller_event_handler.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.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_CONTROLLER_EVENT_HANDLER_H_
 #define CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_CONTROLLER_EVENT_HANDLER_H_
 
 #include <memory>
 
 #include "base/memory/shared_memory.h"
 #include "content/common/content_export.h"
 #include "mojo/public/cpp/system/buffer.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace media {
 class VideoFrame;
 }  // namespace media
 
 namespace content {
 
 typedef int VideoCaptureControllerID;
 
 // VideoCaptureControllerEventHandler is the interface for
 // VideoCaptureController to notify clients about the events such as
 // BufferReady, FrameInfo, Error, etc.
+
+// OnStarted can be forwarded directly, while OnError&OnEnded need to be
+// scheduled to the end of message queue to guarantee some other clearing
+// jobs are done before they are handled.

[chfremer, 2017/02/22 19:13:58]

directly -> synchronously (to use the more precise technical term)

Since we are specifying this for some of the methods, a reader will naturally
also want to know about the remaining methods OnBufferCreated,
OnBufferDestroyed, OnBufferReady?
Can they be forwarded synchronously?

[braveyao, 2017/02/23 00:06:26]

Done.

+
 // TODO(mcasas): https://crbug.com/654176 merge back into VideoCaptureController
 class CONTENT_EXPORT VideoCaptureControllerEventHandler {
  public:
   // An Error has occurred in the VideoCaptureDevice.
   virtual void OnError(VideoCaptureControllerID id) = 0;
 
   // A buffer has been newly created.
   virtual void OnBufferCreated(VideoCaptureControllerID id,
                                mojo::ScopedSharedBufferHandle handle,
                                int length,
                                int buffer_id) = 0;
 
   // A previously created buffer has been freed and will no longer be used.
   virtual void OnBufferDestroyed(VideoCaptureControllerID id,
                                  int buffer_id) = 0;
 
   // A buffer has been filled with a captured VideoFrame.
   virtual void OnBufferReady(VideoCaptureControllerID id,
                              int buffer_id,
                              const scoped_refptr<media::VideoFrame>& frame) = 0;
 
   // The capture session has ended and no more frames will be sent.
   virtual void OnEnded(VideoCaptureControllerID id) = 0;
 
+  // VideoCaptureDevice has successfully started the device.
+  virtual void OnStarted(VideoCaptureControllerID id) = 0;
+
  protected:
   virtual ~VideoCaptureControllerEventHandler() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_CONTROLLER_EVENT_HANDLER_H_