Implement screen capture for android

content/browser/media/capture/content_video_capture_device_core.h

Index: content/browser/media/capture/content_video_capture_device_core.h
diff --git a/content/browser/media/capture/content_video_capture_device_core.h b/content/browser/media/capture/content_video_capture_device_core.h
index f477a157439a33aa845cc0758008cc099a49163b..723a7aef87a9d74d2ca6699e85adbe62e0e36b3c 100644
--- a/content/browser/media/capture/content_video_capture_device_core.h
+++ b/content/browser/media/capture/content_video_capture_device_core.h
@@ -108,19 +108,19 @@ class ThreadSafeCaptureOracle
   gfx::Size capture_size_;
 };
 
-// Keeps track of the video capture source frames and executes copying on the
-// UI BrowserThread.
+// Keeps track of the video capture source frames and executes copying.
 class VideoCaptureMachine {
  public:
   VideoCaptureMachine() {}
   virtual ~VideoCaptureMachine() {}
 
-  // Starts capturing. Returns true if succeeded.
-  // Must be run on the UI BrowserThread.
-  virtual bool Start(const scoped_refptr<ThreadSafeCaptureOracle>& oracle_proxy,
-                     const media::VideoCaptureParams& params) = 0;
+  // Starts capturing.
+  // |callback| is invoked with true if succeeded. Otherwise, with false.
+  virtual void Start(const scoped_refptr<ThreadSafeCaptureOracle>& oracle_proxy,
+                     const media::VideoCaptureParams& params,
+                     const base::Callback<void(bool)> callback) = 0;
 
-  // Stops capturing. Must be run on the UI BrowserThread.
+  // Stops capturing.
   // |callback| is invoked after the capturing has stopped.
   virtual void Stop(const base::Closure& callback) = 0;
 
@@ -173,9 +173,9 @@ class CONTENT_EXPORT ContentVideoCaptureDeviceCore
   // Current lifecycle state.
   State state_;
 
-  // Tracks the CaptureMachine that's doing work on our behalf on the UI thread.
-  // This value should never be dereferenced by this class, other than to
-  // create and destroy it on the UI thread.
+  // Tracks the CaptureMachine that's doing work on our behalf
+  // on the device thread or UI thread.
+  // This value should never be dereferenced by this class.
   scoped_ptr<VideoCaptureMachine> capture_machine_;
 
   // Our thread-safe capture oracle which serves as the gateway to the video