getUserMeida: report device starting states

media/capture/video/video_capture_device.h

Index: media/capture/video/video_capture_device.h
diff --git a/media/capture/video/video_capture_device.h b/media/capture/video/video_capture_device.h
index a716db8665967b41a6af20cf42600324457ff978..8e15cb6a59a443a8be7d7463fb1520b69966edea 100644
--- a/media/capture/video/video_capture_device.h
+++ b/media/capture/video/video_capture_device.h
@@ -214,6 +214,13 @@ class CAPTURE_EXPORT VideoCaptureDevice
     // Returns the current buffer pool utilization, in the range 0.0 (no buffers
     // are in use by producers or consumers) to 1.0 (all buffers are in use).
     virtual double GetBufferPoolUtilization() const = 0;
+
+    // VideoCaptureDevice reports it's successfully started.
+    // This method may be called either synchronously from an invocation of
+    // VideoCaptureDevice::AllocateAndStart() or asynchronously from any thread
+    // after AllocateAndStart() has returned. It is guaranteed to get called
+    // before any video frames are delivered.
+    virtual void OnStarted() = 0;
   };
 
   ~VideoCaptureDevice() override;