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

media/capture/video/video_capture_buffer_pool_impl.h

 // 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.
 
 #ifndef MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_BUFFER_POOL_IMPL_H_
 #define MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_BUFFER_POOL_IMPL_H_
 
 #include <stddef.h>
 
 #include <map>
 
 #include "base/files/file.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/shared_memory.h"
 #include "base/process/process.h"
 #include "base/synchronization/lock.h"
 #include "build/build_config.h"
 #include "media/base/video_frame.h"
 #include "media/capture/capture_export.h"
 #include "media/capture/video/video_capture_buffer_handle.h"
 #include "media/capture/video/video_capture_buffer_pool.h"
 #include "media/capture/video/video_capture_buffer_tracker_factory.h"
 #include "media/capture/video_capture_types.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/gpu_memory_buffer.h"
 
 namespace media {
 
+// This implementation guarantees that, even when creating new instances,
+// a previously used |buffer_id| is never reused without first cycling through
+// the complete int range.
 class CAPTURE_EXPORT VideoCaptureBufferPoolImpl
     : public VideoCaptureBufferPool {
  public:
   explicit VideoCaptureBufferPoolImpl(
       std::unique_ptr<VideoCaptureBufferTrackerFactory> buffer_tracker_factory,
       int count);
 
   // VideoCaptureBufferPool implementation.
   mojo::ScopedSharedBufferHandle GetHandleForInterProcessTransit(
       int buffer_id) override;
@@ skipping 26 matching lines @@
 
   VideoCaptureBufferTracker* GetTracker(int buffer_id);
 
   // The max number of buffers that the pool is allowed to have at any moment.
   const int count_;
 
   // Protects everything below it.
   mutable base::Lock lock_;
 
   // The ID of the next buffer.
-  int next_buffer_id_;
+  static int next_buffer_id_;
 
   // The ID of the buffer last relinquished by the producer (a candidate for
   // resurrection).
   int last_relinquished_buffer_id_;
 
   // The buffers, indexed by the first parameter, a buffer id.
   std::map<int, std::unique_ptr<VideoCaptureBufferTracker>> trackers_;
 
   const std::unique_ptr<VideoCaptureBufferTrackerFactory>
       buffer_tracker_factory_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(VideoCaptureBufferPoolImpl);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_BUFFER_POOL_IMPL_H_