Enable renderer side mixing behind a flag.

content/renderer/media/audio_renderer_mixer_manager.h

Index: content/renderer/media/audio_renderer_mixer_manager.h
diff --git a/content/renderer/media/audio_renderer_mixer_manager.h b/content/renderer/media/audio_renderer_mixer_manager.h
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+++ b/content/renderer/media/audio_renderer_mixer_manager.h
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+// Copyright (c) 2012 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_RENDERER_MEDIA_AUDIO_RENDERER_MIXER_MANAGER_H_
+#define CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_MIXER_MANAGER_H_
+
+#include <map>
+
+#include "base/synchronization/lock.h"
+#include "content/common/content_export.h"
+#include "media/audio/audio_parameters.h"
+
+namespace media {
+class AudioRendererMixer;
+class AudioRendererMixerInput;
+}
+
+namespace content {
+
+// Manages sharing of an AudioRendererMixer among AudioRendererMixerInputs based
+// on their AudioParameters configuration.  Inputs with the same AudioParameters
+// configuration will share a mixer while a new AudioRendererMixer will be
+// lazily created if one with the exact AudioParameters does not exist.
+//
+// There should only be one instance of AudioRendererMixerManager per render
+// thread.
+//
+// TODO(dalecurtis): Right now we require AudioParameters to be an exact match
+// when we should be able to ignore bits per channel since we're only dealing
+// with floats.  However, bits per channel is currently used to interleave the
+// audio data by AudioDevice::AudioThreadCallback::Process for consumption via
+// the shared memory.  See http://crbug.com/114700.
+class CONTENT_EXPORT AudioRendererMixerManager {
+ public:
+  // Construct an instance using the given audio hardware configuration.
+  AudioRendererMixerManager(int hardware_sample_rate, int hardware_buffer_size);
+  ~AudioRendererMixerManager();
+
+  // Creates an AudioRendererMixerInput with the proper callbacks necessary to
+  // retrieve an AudioRendererMixer instance from AudioRendererMixerManager.
+  // Caller must ensure AudioRendererMixerManager outlives the returned input.
+  media::AudioRendererMixerInput* CreateInput();
+
+ private:
+  friend class AudioRendererMixerManagerTest;
+
+  // Returns a mixer instance based on AudioParameters; an existing one if one
+  // with the provided AudioParameters exists or a new one if not.
+  media::AudioRendererMixer* GetMixer(const media::AudioParameters& params);
+
+  // Remove a mixer instance given a mixer if the only other reference is held
+  // by AudioRendererMixerManager.  Every AudioRendererMixer owner must call
+  // this method when it's done with a mixer.
+  void RemoveMixer(const media::AudioParameters& params);
+
+  // Map of AudioParameters to <AudioRendererMixer, Count>.  Count allows
+  // AudioRendererMixerManager to keep track explicitly (v.s. RefCounted which
+  // is implicit) of the number of outstanding AudioRendererMixers.
+  struct AudioRendererMixerReference {
+    media::AudioRendererMixer* mixer;
+    int ref_count;
+  };
+  typedef std::map<media::AudioParameters, AudioRendererMixerReference,
+                   media::AudioParameters::Compare> AudioRendererMixerMap;
+  AudioRendererMixerMap mixers_;
+  base::Lock mixers_lock_;
+
+  // Audio hardware configuration.  Used to construct output AudioParameters for
+  // each AudioRendererMixer instance.
+  int hardware_sample_rate_;
+  int hardware_buffer_size_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioRendererMixerManager);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_MIXER_MANAGER_H_