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

services/video_capture/buffer_tracker_factory_impl.cc

+// 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.
+
+#include "services/video_capture/buffer_tracker_factory_impl.h"
+
+#include "base/memory/ptr_util.h"
+#include "services/video_capture/mojo_shared_memory_buffer_tracker.h"
+
+namespace video_capture {
+
+std::unique_ptr<media::VideoCaptureBufferTracker>
+BufferTrackerFactoryImpl::CreateTracker(media::VideoPixelStorage storage) {
+  switch (storage) {
+    case media::PIXEL_STORAGE_CPU:
+      return base::MakeUnique<MojoSharedMemoryBufferTracker>();
+  }
+  NOTREACHED();
+  return std::unique_ptr<media::VideoCaptureBufferTracker>();
+}
+
+}  // namespace video_capture