Add a virtual beamforming audio device on ChromeOS.

media/audio/audio_parameters.h

Index: media/audio/audio_parameters.h
diff --git a/media/audio/audio_parameters.h b/media/audio/audio_parameters.h
index 3820d8cc3c91de2f3f7168d58074d2b25f8a4072..febae9aa9b35290013e39df3d9fa56020ad605ae 100644
--- a/media/audio/audio_parameters.h
+++ b/media/audio/audio_parameters.h
@@ -57,15 +57,21 @@ class MEDIA_EXPORT AudioParameters {
   };
 
   AudioParameters();
-  AudioParameters(Format format, ChannelLayout channel_layout,
-                  int sample_rate, int bits_per_sample,
-                  int frames_per_buffer);
-  AudioParameters(Format format, ChannelLayout channel_layout,
-                  int sample_rate, int bits_per_sample,
-                  int frames_per_buffer, int effects);
-  AudioParameters(Format format, ChannelLayout channel_layout,
-                  int channels, int sample_rate, int bits_per_sample,
-                  int frames_per_buffer, int effects);
+  AudioParameters(Format format,
+                  ChannelLayout channel_layout,
+                  int sample_rate,
+                  int bits_per_sample,
+                  int frames_per_buffer,
+                  const std::string& mic_positions = "",
+                  int effects = NO_EFFECTS);
+  AudioParameters(Format format,
+                  int channels,
+                  ChannelLayout channel_layout,
+                  int sample_rate,
+                  int bits_per_sample,
+                  int frames_per_buffer,
+                  const std::string& mic_positions = "",
+                  int effects = NO_EFFECTS);

[ajm, 2015/08/26 00:56:09]

Some of the parameters are reordered (channels <-> channel_layout, effects moved
to the end) for type safety with the default parameters. That is, it's harder to
use the wrong int value now.

 
   void Reset(Format format, ChannelLayout channel_layout,

[ajm, 2015/08/26 01:08:18]

I could similarly reorder Reset, but I'll wait for a follow-up CL.

              int channels, int sample_rate, int bits_per_sample,
@@ -102,6 +108,7 @@ class MEDIA_EXPORT AudioParameters {
   int frames_per_buffer() const { return frames_per_buffer_; }
   int channels() const { return channels_; }
   int effects() const { return effects_; }
+  const std::string& mic_positions() const { return mic_positions_; }
 
  private:
   // These members are mutable to support entire struct assignment. They should
@@ -114,6 +121,22 @@ class MEDIA_EXPORT AudioParameters {
 
   int channels_;                  // Number of channels. Value set based on
                                   // |channel_layout|.
+
+  // Whitespace-separated microphone positions using Cartesian coordinates in
+  // meters with ordering x, y, z.
+  // x: the horizontal dimension, with positive to the right from the camera's
+  //    perspective.
+  // y: the depth dimension, with positive forward from the camera's
+  //    perspective.
+  // z: the vertical dimension, with positive upwards.
+  //
+  // Usually, the center of the microphone array will be treated as the origin
+  // (often the position of the camera). The string is formatted as:
+  // "x1 y1 z1 ... zn yn zn" for an n-microphone array.
+  // For example, a two-mic device with 4 cm of horizontal spacing would use:
+  // "-0.02 0 0 0.02 0 0"
+  std::string mic_positions_;
+
   int effects_;                   // Bitmask using PlatformEffectsMask.
 };