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"
+
+using content::AudioDeviceFactory;

[jochen (gone - plz use gerrit), 2012/07/13 08:51:03]

after you've moved the class into namespace content, this is no longer required

[DaleCurtis, 2012/07/13 21:28:33]

Done.

+
+AudioRendererMixerManager::AudioRendererMixerManager() {
+  // DCHECK something static?

[scherkus (not reviewing), 2012/07/13 18:40:16]

wha?

[DaleCurtis, 2012/07/13 21:28:33]

Leftover from an earlier thought process about ensuring only one ARMM is ever in
existence.

+}
+
+AudioRendererMixerManager::~AudioRendererMixerManager() {}

[jochen (gone - plz use gerrit), 2012/07/13 08:51:03]

maybe DCHECK that all mixers have been removed?

[scherkus (not reviewing), 2012/07/13 18:40:16]

yeah DCHECK(mixer_map_.empty()) wouldn't hurt

[DaleCurtis, 2012/07/13 21:28:33]

Done.

+
+scoped_refptr<media::AudioRendererMixerInput>
+AudioRendererMixerManager::CreateInput() {
+  return new media::AudioRendererMixerInput(

[jochen (gone - plz use gerrit), 2012/07/13 08:51:03]

please add a comment in the header that the caller must ensure that the
AudioRenderMixerManager outlives the return value

[DaleCurtis, 2012/07/13 21:28:33]

Done.

+      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()) {
+    // Increment the reference count.

[scherkus (not reviewing), 2012/07/13 18:40:16]

comment ain't useful

[DaleCurtis, 2012/07/13 21:28:33]

Done.

+    it->second.second++;
+    return it->second.first;
+  }
+
+  // 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?
+  media::AudioRendererMixer* mixer = new media::AudioRendererMixer(
+      params, media::AudioParameters(
+          media::AudioParameters::AUDIO_PCM_LOW_LATENCY,
+          params.channel_layout(), media::GetAudioHardwareSampleRate(), 16,
+          media::GetAudioHardwareBufferSize()),
+      AudioDeviceFactory::Create());
+  mixer_map_[params] = std::make_pair(mixer, 1);
+  return 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());
+
+  // Remove the reference.

[jochen (gone - plz use gerrit), 2012/07/13 08:51:03]

that comment doesn't add any value

[DaleCurtis, 2012/07/13 21:28:33]

Done.

+  it->second.second--;
+
+  // Only remove the mixer if AudioRendererMixerManager is the last owner.
+  if (it->second.second == 0) {
+    delete it->second.first;
+    mixer_map_.erase(it);
+  }
+}