Enable renderer side mixing behind a flag.

content/renderer/media/audio_renderer_mixer_manager.cc

+// 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.
+
+#include "content/renderer/media/audio_renderer_mixer_manager.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "content/renderer/media/audio_device_factory.h"
+#include "media/audio/audio_util.h"
+#include "media/base/audio_renderer_mixer.h"
+#include "media/base/audio_renderer_mixer_input.h"
+
+namespace content {
+
+AudioRendererMixerManager::AudioRendererMixerManager() {}
+
+AudioRendererMixerManager::~AudioRendererMixerManager() {
+  DCHECK(mixer_map_.empty());
+}
+
+media::AudioRendererMixerInput* AudioRendererMixerManager::CreateInput() {
+  return new media::AudioRendererMixerInput(
+      base::Bind(
+          &AudioRendererMixerManager::GetMixer, base::Unretained(this)),
+      base::Bind(
+          &AudioRendererMixerManager::RemoveMixer, base::Unretained(this)));
+}
+
+media::AudioRendererMixer* AudioRendererMixerManager::GetMixer(
+    const media::AudioParameters& params) {
+  base::AutoLock auto_lock(mixer_map_lock_);
+
+  AudioRendererMixerMap::iterator it = mixer_map_.find(params);
+  if (it != mixer_map_.end()) {
+    it->second.ref_count++;
+    return it->second.mixer;
+  }
+
+  // Create output parameters for passing on to the output sink.
+  // TODO(dalecurtis): Set format and buffer size in AudioRendererImpl.
+  // TODO(dalecurtis): We don't care about the hardware in the ARMM tests, but
+  // is it okay for unit tests to call these methods?

[scherkus (not reviewing), 2012/07/13 23:17:38]

as discussed offline you can change this to reference http://crbug.com/137326

[DaleCurtis, 2012/07/14 00:39:26]

Done.

+  AudioRendererMixerReference mixer_reference = {
+      new media::AudioRendererMixer(

[scherkus (not reviewing), 2012/07/13 23:17:38]

nit for code clarity -- can you break out these objects into separate
statements?

media::AudioParameters output_params = ...;
media::ARM mixer = ...;
reference = { mixer, 1 };

[DaleCurtis, 2012/07/14 00:39:26]

Done.

+          params, media::AudioParameters(
+              media::AudioParameters::AUDIO_PCM_LOW_LATENCY,
+              params.channel_layout(), media::GetAudioHardwareSampleRate(), 16,
+              media::GetAudioHardwareBufferSize()),
+          AudioDeviceFactory::Create()),
+      1};
+  mixer_map_[params] = mixer_reference;
+  return mixer_reference.mixer;
+}
+
+void AudioRendererMixerManager::RemoveMixer(
+    const media::AudioParameters& params) {
+  base::AutoLock auto_lock(mixer_map_lock_);
+
+  AudioRendererMixerMap::iterator it = mixer_map_.find(params);
+  DCHECK(it != mixer_map_.end());
+
+  // Only remove the mixer if AudioRendererMixerManager is the last owner.
+  it->second.ref_count--;
+  if (it->second.ref_count == 0) {
+    delete it->second.mixer;
+    mixer_map_.erase(it);
+  }
+}
+
+}  // namespace content