Add AudioStreamRegistry. Move stream counting logic

content/browser/renderer_host/media/audio_stream_registry.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_H_
+#define CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_STREAM_REGISTRY_H_
+
+namespace content {
+
+// This class tracks all the input and output streams and enables stream
+// counting and debug recording controll for the RenderProcessHost. Methods
+// may only be called on the IO thread.
+class AudioStreamRegistry {
+ public:
+  class Stream {
+   public:
+    virtual ~Stream() {}
+    /*
+    virtual void EnableDebugRecording() = 0;
+    virtual void DisableDebugRecording() = 0;
+    */
+  };
+
+  virtual ~AudioStreamRegistry() {}
+
+  // Streams must be removed before destruction.
+  // virtual void RegisterInputStream(Stream* stream) = 0;
+  virtual void RegisterOutputStream(Stream* stream) = 0;
+  // virtual void DeregisterInputStream(Stream* stream) = 0;
+  virtual void DeregisterOutputStream(Stream* stream) = 0;
+
+  virtual void OutputStreamStateChanged(bool playing) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_STREAM_REGISTRY_H_