Introduce VideoFrameScheduler{Impl}.

media/filters/video_frame_scheduler.h

+// Copyright 2014 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 MEDIA_FILTERS_VIDEO_FRAME_SCHEDULER_H_
+#define MEDIA_FILTERS_VIDEO_FRAME_SCHEDULER_H_
+
+#include "base/callback.h"
+#include "base/memory/ref_counted.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+class VideoFrame;
+
+// Defines an abstract video frame scheduler that is capable of managing the
+// display of video frames at explicit times.
+class MEDIA_EXPORT VideoFrameScheduler {
+ public:
+  VideoFrameScheduler() {}
+  virtual ~VideoFrameScheduler() {}
+
+  enum Reason {
+    DISPLAYED,  // Frame was displayed.
+    DROPPED,    // Frame was dropped.
+    RESET,      // Scheduler was reset and frames are being returned.

[acolwell GONE FROM CHROMIUM, 2014/04/14 21:17:59]

nit: Frames are returned in all cases so this comment seems a little misleading.
How about something along the lines of "Scheduler was reset before the frame was
scheduled for display."

[scherkus (not reviewing), 2014/04/14 21:35:31]

Done.

+  };
+  typedef base::Callback<void(const scoped_refptr<VideoFrame>&, Reason)> DoneCB;
+
+  // Schedule |frame| to be displayed at |wall_ticks|, firing |done_cb| when
+  // the scheduler has finished with the frame.
+  //
+  // Assuming Reset() wasn't called, frames will be returned as either DISPLAYED
+  // or DROPPED.

[acolwell GONE FROM CHROMIUM, 2014/04/14 21:17:59]

This part of the comment doesn't seem that helpful since frames are returned in
all cases right?

[scherkus (not reviewing), 2014/04/14 21:35:31]

yeah -- removed

+  virtual void ScheduleVideoFrame(const scoped_refptr<VideoFrame>& frame,
+                                  base::TimeTicks wall_ticks,
+                                  const DoneCB& done_cb) = 0;
+
+  // Causes the scheduler to release all previously scheduled frames. Frames
+  // will be returned as RESET.
+  virtual void Reset() = 0;
+};
+
+}  // namespace media
+
+#endif  // MEDIA_FILTERS_VIDEO_FRAME_SCHEDULER_H_