[Mojo Video Capture] Retire buffers when Android Chromium goes to the background

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"
 #include "build/build_config.h"
 #include "media/capture/video/video_capture_buffer_handle.h"
 #include "media/capture/video/video_capture_buffer_tracker.h"
 #include "ui/gfx/buffer_format_util.h"
 
 namespace media {
 
+int VideoCaptureBufferPoolImpl::next_buffer_id_ = 0;
+
 VideoCaptureBufferPoolImpl::VideoCaptureBufferPoolImpl(
     std::unique_ptr<VideoCaptureBufferTrackerFactory> buffer_tracker_factory,
     int count)
     : count_(count),
-      next_buffer_id_(0),
       last_relinquished_buffer_id_(kInvalidId),
       buffer_tracker_factory_(std::move(buffer_tracker_factory)) {
   DCHECK_GT(count, 0);
 }
 
 VideoCaptureBufferPoolImpl::~VideoCaptureBufferPoolImpl() {}
 
 mojo::ScopedSharedBufferHandle
 VideoCaptureBufferPoolImpl::GetHandleForInterProcessTransit(int buffer_id) {
   base::AutoLock lock(lock_);
@@ skipping 208 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