Introduce AudioHardwareConfig for renderer side audio device info.

content/renderer/media/renderer_audio_hardware_config.h

+// Copyright (c) 2013 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_RENDERER_AUDIO_HARDWARE_CONFIG_H_
+#define CONTENT_RENDERER_MEDIA_RENDERER_AUDIO_HARDWARE_CONFIG_H_
+
+#include "base/compiler_specific.h"

[henrika (OOO until Aug 14), 2013/01/29 10:46:49]

Why do you need this one here?

[DaleCurtis, 2013/01/30 01:31:06]

Necessary for the DISALLOW_COPY_AND_ASSIGN() macro.

+#include "base/synchronization/lock.h"
+#include "content/common/content_export.h"
+#include "media/base/audio_hardware_config.h"
+
+namespace content {
+
+// Provides access to the audio hardware configuration from the renderer side.
+class CONTENT_EXPORT RendererAudioHardwareConfig
+    : public media::AudioHardwareConfig {
+ public:
+  // Must be constructed on the render thread.  RendererAudioHardwareConfig
+  // sends a synchronous IPC to retrieve the audio hardware configuration; once
+  // complete accessors and updaters may be called from any thread.
+  RendererAudioHardwareConfig();
+  virtual ~RendererAudioHardwareConfig();
+
+  // Constructor for tests which don't have a render thread.
+  RendererAudioHardwareConfig(int output_buffer_size, int output_sample_rate,

[henrika (OOO until Aug 14), 2013/01/29 10:46:49]

Should it be public?

[DaleCurtis, 2013/01/30 01:31:06]

Easier if it is. Otherwise there's a bunch of ugly friend testing necessary. I
could go either way.

+                              int input_sample_rate,
+                              media::ChannelLayout input_channel_layout);
+
+  // Accessors for the currently cached hardware configuration.  Safe to call
+  // from any thread.
+  virtual int GetOutputBufferSize() OVERRIDE;
+  virtual int GetOutputSampleRate() OVERRIDE;
+  virtual int GetInputSampleRate() OVERRIDE;
+  virtual media::ChannelLayout GetInputChannelLayout() OVERRIDE;
+
+  // Allows callers to update the cached values for either input or output.  The
+  // values are paired under the assumption that these values will only be set
+  // after an input or output device change respectively.  Safe to call from
+  // any thread.
+  void UpdateInputConfig(int sample_rate, media::ChannelLayout channel_layout);

[henrika (OOO until Aug 14), 2013/01/29 10:46:49]

OK, now I get it. Seen as implementation detail and moved from the interface.

+  void UpdateOutputConfig(int buffer_size, int sample_rate);
+
+ private:
+  // Cached values; access is protected by |config_lock_|.
+  base::Lock config_lock_;

[henrika (OOO until Aug 14), 2013/01/29 10:46:49]

How is this class used today? Are all methods only called from the render thread
and if so do we really need the lock? 

[DaleCurtis, 2013/01/29 19:36:00]

AudioRendererMixerManager::GetMixer() may be called from the media thread, which
is why this class offers thread safety.  Currently, this patch set always calls
from the render thread, but ideally AudioMessageFilter can call the update
method from the IO thread thanks to this lock.

+  int output_buffer_size_;
+  int output_sample_rate_;
+  int input_sample_rate_;
+  media::ChannelLayout input_channel_layout_;
+
+  DISALLOW_COPY_AND_ASSIGN(RendererAudioHardwareConfig);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_RENDERER_AUDIO_HARDWARE_CONFIG_H_