audio API: Use an enum for audio device device type

extensions/common/api/audio.idl

 // 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.
 
 // The <code>chrome.audio</code> API is provided to allow users to
 // get information about and control the audio devices attached to the
 // system. This API is currently only implemented for ChromeOS.
 namespace audio {
 
   // Type of stream an audio device provides.
   enum StreamType {
     INPUT,
     OUTPUT
   };
 
+  // Available audio device types.
+  enum DeviceType {
+    HEADPHONE,
+    MIC,
+    USB,
+    BLUETOOTH,
+    HDMI,
+    INTERNAL_SPEAKER,
+    INTERNAL_MIC,
+    FRONT_MIC,
+    REAR_MIC,
+    KEYBOARD_MIC,
+    HOTWORD,
+    LINEOUT,
+    POST_MIX_LOOPBACK,
+    POST_DSP_LOOPBACK,
+    OTHER
+  };
+
   dictionary OutputDeviceInfo {
     // The unique identifier of the audio output device.
     DOMString id;
     // The user-friendly name (e.g. "Bose Amplifier").
     DOMString name;
     // True if this is the current active device.
     boolean isActive;
     // True if this is muted.
     boolean isMuted;
     // The output volume ranging from 0.0 to 100.0.
@@ skipping 13 matching lines @@
     double gain;
   };
 
   dictionary AudioDeviceInfo {
     // The unique identifier of the audio device.
     DOMString id;
     // Stream type associated with this device.
     StreamType streamType;
     // True for input device; false for output device.
     [deprecated="Use |streamType|."] boolean isInput;
-    // Type of the device, including "INTERNAL_SPEAKER", "INTERNAL_MIC",
-    // "HEADPHONE", "USB", "BLUETOOTH", "HDMI", "MIC", "KEYBOARD_MIC",
-    // "AOKR", and "OTHER".
-    DOMString deviceType;
+    // Type of the device.
+    DeviceType deviceType;
     // The user-friendly name (e.g. "USB Microphone").
     DOMString displayName;
     // Device name.
     DOMString deviceName;
     // True if this is the current active device.
     boolean isActive;
     // True if this is muted.
     boolean isMuted;
     // The sound level of the device, volume for output, gain for input.
     long level;
@@ skipping 89 matching lines @@
     // Note that mute state is system-wide and the new value applies to every
     // audio device with specified stream type.
     static void onMuteChanged(MuteChangedEvent event);
 
     // Fired when audio devices change, either new devices being added, or
     // existing devices being removed.
     // |devices|: List of all present audio devices after the change.
     static void OnDevicesChanged(AudioDeviceInfo[] devices);
   };
 };