Add AudioStreamRegistry. Move stream counting logic

content/browser/renderer_host/media/audio_stream_registry_impl.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 CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_STREAM_REGISTRY_IMPL_H_
+#define CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_STREAM_REGISTRY_IMPL_H_
+
+#include <map>
+#include <memory>
+#include <set>
+
+#include "base/atomic_ref_count.h"
+#include "base/files/file_path.h"
+#include "base/macros.h"
+#include "base/threading/thread_checker.h"
+#include "content/browser/renderer_host/media/audio_stream_registry.h"
+#include "content/common/content_export.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace content {
+
+class CONTENT_EXPORT AudioStreamRegistryImpl : public AudioStreamRegistry {
+ public:
+  explicit AudioStreamRegistryImpl(int render_process_id);
+  ~AudioStreamRegistryImpl() override;
+
+  using UniquePtr =
+      std::unique_ptr<AudioStreamRegistryImpl, BrowserThread::DeleteOnIOThread>;
+
+  static UniquePtr Create(int render_process_id);
+
+  // Indicates whether there is an output stream currently playing.
+  // May be called from any thread.
+  bool HasActiveAudio();
+
+#if BUILDFLAG(ENABLE_WEBRTC)
+  void EnableDebugRecording(const base::FilePath& base_file_path);
+  void DisableDebugRecording();
+#endif  // BUILDFLAG(ENABLE_WEBRTC)
+
+  // Streams must be removed before this object is destructed.
+  // void RegisterInputStream(Stream* stream) override;

[o1ka, 2017/01/10 11:47:40]

Add TODOs instead of commented out methods? (here, and there was some other
place I think)

+  void RegisterOutputStream(Stream* stream) override;
+  // void DeregisterInputStream(Stream* stream) override;
+  void DeregisterOutputStream(Stream* stream) override;
+
+  void OutputStreamStateChanged(Stream* stream, bool playing) override;
+
+  // Resets the thread checker for AudioStreamsTracker. Needed when using
+  // real threads when testing.
+  static void DetachAudioStreamsTrackerFromThreadForTesting();
+
+ private:
+  using StreamSet = std::set<Stream*>;
+
+  size_t max_simultaneous_output_streams_ = 0;
+  const int render_process_id_;
+  base::AtomicRefCount num_playing_output_streams_ = 0;
+  // StreamSet input_streams_;
+  StreamSet output_streams_;
+
+#if BUILDFLAG(ENABLE_WEBRTC)
+  // If debug recoding is active, this is the base file path used.
+  base::FilePath debug_recording_path_;
+#endif  // BUILDFLAG(ENABLE_WEBRTC)
+
+#if DCHECK_IS_ON()
+  std::map<Stream*, bool> stream_currently_playing_;

[o1ka, 2017/01/10 11:47:40]

How about to always have the current status (=map instead of set)? 
BTW vector will be more efficient in both cases, but up to you.

+#endif
+
+  DISALLOW_COPY_AND_ASSIGN(AudioStreamRegistryImpl);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_STREAM_REGISTRY_IMPL_H_