Prime the landing pad for the new video rendering pipeline.

media/blink/video_frame_compositor.h

Index: media/blink/video_frame_compositor.h
diff --git a/media/blink/video_frame_compositor.h b/media/blink/video_frame_compositor.h
index 9e46663e34f74ef3d51ba96269b03addac9259f2..02b6077f9605ff25029cfb08da5adefc8c3808e6 100644
--- a/media/blink/video_frame_compositor.h
+++ b/media/blink/video_frame_compositor.h
@@ -7,24 +7,45 @@
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/lock.h"
 #include "cc/layers/video_frame_provider.h"
 #include "media/base/media_export.h"
+#include "media/base/video_renderer_sink.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace media {
 class VideoFrame;
 
-// VideoFrameCompositor handles incoming frames by notifying the compositor and
-// dispatching callbacks when detecting changes in video frames.
+// VideoFrameCompositor acts as a bridge between the media and cc layers for
+// rendering video frames. I.e. a media::VideoRenderer will talk to this class
+// from the media side, while a cc::VideoFrameProvider::Client will talk to it
+// from the cc side.
 //
-// Typical usage is to deliver ready-to-be-displayed video frames to
-// UpdateCurrentFrame() so that VideoFrameCompositor can take care of tracking
-// changes in video frames and firing callbacks as needed.
+// This class is responsible for requesting new frames from a video renderer in
+// response to requests from the VFP::Client. Since the VFP::Client may stop
+// issuing requests in response to visibility changes it is also responsible for
+// ensuring the "freshness" of the current frame for programmatic frame
+// requests; e.g., Canvas.drawImage() requests
 //
-// VideoFrameCompositor must live on the same thread as the compositor.
+// This class is also responsible for detecting frames dropped by the compositor
+// after rendering and signaling that information to a RenderCallback. It
+// detects frames not dropped by verifying each GetCurrentFrame() is followed
+// by a PutCurrentFrame() before the next UpdateCurrentFrame() call.
+//
+// VideoRenderSink::RenderCallback implementations must call Start() and Stop()
+// once new frames are expected or are no longer expected to be ready; this data
+// is relayed to the compositor to avoid extraneous callbacks.
+//
+// VideoFrameCompositor must live on the same thread as the compositor, though
+// it may be constructed on any thread.
 class MEDIA_EXPORT VideoFrameCompositor
-    : NON_EXPORTED_BASE(public cc::VideoFrameProvider) {
+    : public VideoRendererSink,
+      NON_EXPORTED_BASE(public cc::VideoFrameProvider) {
  public:
+  // |compositor_task_runner| is the task runner on which this class will live,
+  // though it may be constructed on any thread.
+  //
   // |natural_size_changed_cb| is run with the new natural size of the video
   // frame whenever a change in natural size is detected. It is not called the
   // first time UpdateCurrentFrame() is called. Run on the same thread as the
@@ -34,31 +55,62 @@ class MEDIA_EXPORT VideoFrameCompositor
   // called the first time UpdateCurrentFrame() is called. Run on the same
   // thread as the caller of UpdateCurrentFrame().
   //
-  // TODO(scherkus): Investigate the inconsistency between the callbacks with
+  // TODO(dalecurtis): Investigate the inconsistency between the callbacks with
   // respect to why we don't call |natural_size_changed_cb| on the first frame.
   // I suspect it was for historical reasons that no longer make sense.
   VideoFrameCompositor(
+      const scoped_refptr<base::SingleThreadTaskRunner>& compositor_task_runner,
       const base::Callback<void(gfx::Size)>& natural_size_changed_cb,
       const base::Callback<void(bool)>& opacity_changed_cb);
+
+  // Destruction must happen on the compositor thread; Stop() must have been
+  // called before destruction starts.
   ~VideoFrameCompositor() override;
 
-  // cc::VideoFrameProvider implementation.
+  // Returns |current_frame_| if it was refreshed recently; otherwise, if
+  // |callback_| is available, requests a new frame and returns that one.
+  //
+  // This is required for programmatic frame requests where the compositor may
+  // have stopped issuing UpdateCurrentFrame() callbacks in response to
+  // visibility changes in the output layer.
+  scoped_refptr<VideoFrame> GetCurrentFrameAndUpdateIfStale();
+
+  // cc::VideoFrameProvider implementation. These methods must be called on the
+  // |compositor_task_runner_|.
   void SetVideoFrameProviderClient(
       cc::VideoFrameProvider::Client* client) override;
+  bool UpdateCurrentFrame(base::TimeTicks deadline_min,
+                          base::TimeTicks deadline_max) override;
   scoped_refptr<VideoFrame> GetCurrentFrame() override;
-  void PutCurrentFrame(const scoped_refptr<VideoFrame>& frame) override;
+  void PutCurrentFrame() override;
 
-  // Updates the current frame and notifies the compositor.
-  void UpdateCurrentFrame(const scoped_refptr<VideoFrame>& frame);
+  // VideoRendererSink implementation. These methods must be called from the
+  // same thread (typically the media thread).
+  void Start(RenderCallback* callback) override;
+  void Stop() override;
+  void PaintFrameUsingOldRenderingPath(
+      const scoped_refptr<VideoFrame>& frame) override;
 
  private:
+  // Called on the compositor thread to start or stop rendering if rendering was
+  // previously started or stopped before we had a |callback_|.
+  void OnRendererStateUpdate();
+
+  scoped_refptr<base::SingleThreadTaskRunner> compositor_task_runner_;
+
+  // These callbacks are executed on the compositor thread.
   base::Callback<void(gfx::Size)> natural_size_changed_cb_;
   base::Callback<void(bool)> opacity_changed_cb_;
 
+  // These values are only set and read on the compositor thread.
   cc::VideoFrameProvider::Client* client_;
-
   scoped_refptr<VideoFrame> current_frame_;
 
+  // These values are updated and read from the media and compositor threads.
+  base::Lock lock_;
+  bool rendering_;
+  VideoRendererSink::RenderCallback* callback_;
+
   DISALLOW_COPY_AND_ASSIGN(VideoFrameCompositor);
 };