Add AudioStreamRegistry. Move stream counting logic

content/browser/renderer_host/media/audio_stream_registry_impl.h

Index: content/browser/renderer_host/media/audio_stream_registry_impl.h
diff --git a/content/browser/renderer_host/media/audio_stream_registry_impl.h b/content/browser/renderer_host/media/audio_stream_registry_impl.h
new file mode 100644
index 0000000000000000000000000000000000000000..d7f93062051bf64de05ed4df90c138b7d892d8bc
--- /dev/null
+++ b/content/browser/renderer_host/media/audio_stream_registry_impl.h
@@ -0,0 +1,53 @@
+// 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 <unordered_set>
+
+#include "base/atomic_ref_count.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"
+
+namespace content {
+
+class CONTENT_EXPORT AudioStreamRegistryImpl : public AudioStreamRegistry {
+ public:
+  explicit AudioStreamRegistryImpl(int render_process_id);
+  ~AudioStreamRegistryImpl() override;
+
+  // Indicates whether there is an output stream currently playing.
+  // May be called from any thread.
+  bool HasActiveAudio();
+
+  // TODO(maxmorin): Enable/disable debug recording for all tracked streams.
+  /*void EnableDebugRecording();
+  void DisableDebugRecording();*/
+
+  // Streams must be removed before this object is destructed.
+  // void RegisterInputStream(Stream* stream) override;
+  void RegisterOutputStream(Stream* stream) override;
+  // void DeregisterInputStream(Stream* stream) override;
+  void DeregisterOutputStream(Stream* stream) override;
+
+  void OutputStreamStateChanged(bool playing) override;
+
+ private:
+  using StreamSet = std::unordered_set<Stream*>;

[o1ka, 2016/12/16 09:48:16]

Have you considered using <set>? We hardly ever have more than 250 streams and
pointer comparison is cheaper than hash calculation.

[Max Morin, 2016/12/19 16:29:03]

Done.

+
+  const int render_process_id_;
+  size_t max_simultaneous_output_streams_ = 0;
+  base::AtomicRefCount num_playing_output_streams_ = 0;
+  // StreamSet input_streams_;
+  StreamSet output_streams_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioStreamRegistryImpl);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_STREAM_REGISTRY_IMPL_H_