[Mojo Video Capture] Simplify media::VideoCaptureDevice::Client:Buffer to a struct

services/video_capture/mojo_shared_memory_buffer_tracker.h

-// Copyright 2016 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 SERVICES_VIDEO_CAPTURE_MOJO_SHARED_MEMORY_BUFFER_TRACKER_H_
-#define SERVICES_VIDEO_CAPTURE_MOJO_SHARED_MEMORY_BUFFER_TRACKER_H_
-
-#include "media/capture/video/video_capture_buffer_tracker.h"
-#include "media/mojo/common/mojo_shared_buffer_video_frame.h"
-
-namespace video_capture {
-
-// Tracker specifics for MojoSharedMemory.
-class MojoSharedMemoryBufferTracker final
-    : public media::VideoCaptureBufferTracker {
- public:
-  MojoSharedMemoryBufferTracker();
-  ~MojoSharedMemoryBufferTracker() override;
-
-  // Implementation of media::VideoCaptureBufferTracker
-  bool Init(const gfx::Size& dimensions,
-            media::VideoPixelFormat format,
-            media::VideoPixelStorage storage_type,
-            base::Lock* lock) override;
-  std::unique_ptr<media::VideoCaptureBufferHandle> GetBufferHandle() override;
-  mojo::ScopedSharedBufferHandle GetHandleForTransit() override;
-
- private:
-  friend class MojoSharedMemoryBufferHandle;
-
-  scoped_refptr<media::MojoSharedBufferVideoFrame> frame_;
-  size_t mapped_size_;
-};
-
-}  // namespace video_capture
-
-#endif  // SERVICES_VIDEO_CAPTURE_MOJO_SHARED_MEMORY_BUFFER_TRACKER_H_