Add video frame recording capability to Chromoting hosts.

remoting/host/video_frame_recorder.h

Index: remoting/host/video_frame_recorder.h
diff --git a/remoting/host/video_frame_recorder.h b/remoting/host/video_frame_recorder.h
index c204c9ac39cdbdd875ebdc6f22bbb02071597ca7..9d317229459f0075e233f6b0c666fcc73063cabe 100644
--- a/remoting/host/video_frame_recorder.h
+++ b/remoting/host/video_frame_recorder.h
@@ -23,7 +23,7 @@ class VideoEncoder;
 
 // Allows sequences of DesktopFrames passed to a VideoEncoder to be recorded.
 //
-// VideoFrameRecorder is design to support applications which use a dedicated
+// VideoFrameRecorder is designed to support applications which use a dedicated
 // thread for video encoding, but need to manage that process from a "main"
 // or "control" thread.
 //
@@ -50,9 +50,14 @@ class VideoFrameRecorder {
 
   // Wraps the supplied VideoEncoder, returning a replacement VideoEncoder that
   // will route frames to the recorder, as well as passing them for encoding.
-  // This may be called at most once on each VideoFrameRecorder instance.
+  // The caller must delete the previous recording VideoEncoder, or call
+  // DetachVideoEncoderWrapper() before calling WrapVideoEncoder() to create
+  // a new wrapper.

[Jamie, 2014/08/01 19:53:51]

This seems fragile. Why can't Wrap call Detach automatically? Or are you relying
on the DCHECK to catch bad callers?

[Wez, 2014/08/01 22:33:56]

If you create a second wrapper then it'll replace the existing one, which will
stop having its frames recorded. I think it's preferable that the caller
indicate via Detach...() that that behaviour is acceptable.

   scoped_ptr<VideoEncoder> WrapVideoEncoder(scoped_ptr<VideoEncoder> encoder);
 
+  // Detaches the existing VideoEncoder wrapper, stopping it from recording.
+  void DetachVideoEncoderWrapper();
+
   // Enables/disables frame recording. Frame recording is initially disabled.
   void SetEnableRecording(bool enable_recording);