Redesign the copresence audio handlers.

components/copresence/public/copresence_constants.h

 // Copyright 2014 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 COMPONENTS_COPRESENCE_PUBLIC_COPRESENCE_CONSTANTS_
 #define COMPONENTS_COPRESENCE_PUBLIC_COPRESENCE_CONSTANTS_
 
 #include "media/base/channel_layout.h"
 
 namespace copresence {
 
 // Audio constants. Currently used from the AudioPlayer/AudioRecorder.
 // TODO(rkc): Make these values configurable then remove them from here.
 // Number of repetitions of the audio token in one sequence of samples.
 extern const int kDefaultRepetitions;
 
 // The default sample rate. We need to ensure that both the recorder and the
 // player on _all platforms use the same rate.
 extern const float kDefaultSampleRate;
 extern const int kDefaultBitsPerSample;
 
 // 18500 for ultrasound, needs to be consistent between platforms.
 extern const float kDefaultCarrierFrequency;
 
 // The next two really need to be configurable since they don't need to be
 // consistent across platforms, or even playing/recording.
 extern const int kDefaultChannels;
 extern const media::ChannelLayout kDefaultChannelLayout;
 
+// These constants are used from everywhere.
+// Particularly, these are used to index the directive lists in the
+// audio manager, so do not change these enums without changing
+// audio_directive_list.[h|cc].
+enum AudioType {
+  AUDIBLE = 0,
+  INAUDIBLE = 1,
+  BOTH = 2,
+  UNKNOWN = 3,

[Daniel Erat, 2014/10/22 16:34:35]

might've mentioned this already, but "UNKNOWN" seems like an overly-vague value
to put at the top level of the copresence namespace. i think it'd be better to
rename these to AUDIO_AUDIBLE, AUDIO_INAUDIBLE, AUDIO_BOTH, and AUDIO_UNKNOWN
(or AUDIO_TYPE_*).

[rkc, 2014/10/22 18:21:48]

So the enum name is the documentation that this is an audio type. If it isn't
clear at places due to using the enum directly, we can just add
AudioType::UNKNOWN or AudioType::AUDIBLE to achieve the same effect? I believe
this is now legal in C++11?

[Daniel Erat, 2014/10/22 18:32:40]

ah, i didn't know about the c++11 angle. my main concern was just that using
UNKNOWN here would make it difficult to figure out the types of arguments passed
by callers and prevent other enums in the namespace from using UNKNOWN.

[rkc, 2014/10/22 19:28:46]

Ah yes, that would still be a problem even despite scoping. C++ won't let us
declare two different values, despite the fact that people can scope enums
(since unscoped enums are still allowed anyway).

Okay so at least renaming UNKNOWN makes sense since it _is a common type that we
may conflict. AUDIBLE/INAUDIBLE and BOTH are fairly unlikely to develop
conflicts in this namespace.

+};
+
 }  // namespace copresence
 
 #endif  // COMPONENTS_COPRESENCE_PUBLIC_COPRESENCE_CONSTANTS_