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

media/capture/video/video_capture_buffer_pool_impl.cc

 // Copyright (c) 2013 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 "media/capture/video/video_capture_buffer_pool_impl.h"
 
 #include <memory>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 22 matching lines @@
 
   VideoCaptureBufferTracker* tracker = GetTracker(buffer_id);
   if (!tracker) {
     NOTREACHED() << "Invalid buffer_id.";
     return mojo::ScopedSharedBufferHandle();
   }
   return tracker->GetHandleForTransit();
 }
 
 std::unique_ptr<VideoCaptureBufferHandle>
-VideoCaptureBufferPoolImpl::GetBufferHandle(int buffer_id) {
+VideoCaptureBufferPoolImpl::GetReadWriteAccess(int buffer_id) {
   base::AutoLock lock(lock_);
 
   VideoCaptureBufferTracker* tracker = GetTracker(buffer_id);
   if (!tracker) {
     NOTREACHED() << "Invalid buffer_id.";
-    return std::unique_ptr<VideoCaptureBufferHandle>();
+    return nullptr;
   }
 
-  DCHECK(tracker->held_by_producer());
-  return tracker->GetBufferHandle();
+  return tracker->GetReadWriteAccess();
 }
 
 int VideoCaptureBufferPoolImpl::ReserveForProducer(
     const gfx::Size& dimensions,
     media::VideoPixelFormat format,
     media::VideoPixelStorage storage,
     int frame_feedback_id,
     int* buffer_id_to_drop) {
   base::AutoLock lock(lock_);
   return ReserveForProducerInternal(dimensions, format, storage,
@@ skipping 165 matching lines @@
   return buffer_id;
 }
 
 VideoCaptureBufferTracker* VideoCaptureBufferPoolImpl::GetTracker(
     int buffer_id) {
   auto it = trackers_.find(buffer_id);
   return (it == trackers_.end()) ? nullptr : it->second.get();
 }
 
 }  // namespace media