Add ability to retrieve capabilities for audio input devices to MediaDevicesDispatcherHost.

content/common/media/media_devices.mojom

 // Copyright 2016 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.
 
 module mojom;
 
 import "media/capture/mojo/video_capture_types.mojom";
+import "media/mojo/interfaces/audio_parameters.mojom";
 import "url/mojo/origin.mojom";
 
 [Native]
 enum MediaDeviceType;
 
 [Native]
 struct MediaDeviceInfo;
 
 // The values for this enum match the ones defined in
 // https://w3c.github.io/mediacapture-main/#def-constraint-facingMode
 // with the addition of NONE, which would map to the empty string in
 // JavaScript.
 enum FacingMode {
   NONE,
   USER,
   ENVIRONMENT,
   LEFT,
   RIGHT
 };
 
 struct VideoInputDeviceCapabilities {
   string device_id;
   array<media.mojom.VideoCaptureFormat> formats;
   FacingMode facing_mode;
 };
 
+struct AudioInputDeviceCapabilities {
+  string device_id;
+  media.mojom.AudioParameters parameters;
+};
+
 // This object lives in the browser and is responsible for processing device
 // enumeration requests and managing subscriptions for device-change
 // notifications.
 interface MediaDevicesDispatcherHost {
   // The reply always contains NUM_MEDIA_DEVICE_TYPES elements.
   // The result is indexed by device type as defined in 
   // content/common/media/media_devices.h.
   EnumerateDevices(bool request_audio_input,
                    bool request_video_input,
                    bool request_audio_output,
                    url.mojom.Origin security_origin)
                        => (array<array<MediaDeviceInfo>> enumeration);
-  
+
   // Returns a list of video devices and their capabilities.
   // If there is a user-preferred device, it is the first in the result.
   // The result of this function is intended for the implementation details
   // of algorithms such as settings selection for getUserMedia.
-  // Do not expose the data contained in result of this function to JavaScript.
+  // Do not expose the data contained in the result of this function to
+  // JavaScript.
   GetVideoInputCapabilities(url.mojom.Origin security_origin)
       => (array<VideoInputDeviceCapabilities> video_input_device_capabilities);
 
+  // Returns a list of audio input devices and their capabilities.
+  // If there is a user-preferred device, it is the first in the result.
+  // Otherwise, the system-default device is the first in the result.
+  // The result of this function is intended for the implementation details
+  // of algorithms such as settings selection for getUserMedia.
+  // Do not expose the data contained in the result of this function to
+  // JavaScript.
+  GetAudioInputCapabilities(url.mojom.Origin security_origin)

[Mike West, 2017/05/09 09:30:37]

Do you need to pass in an origin? Shouldn't the browser be able to figure out
what origin triggered the request by looking at the frame tree?

[Guido Urdaneta, 2017/05/09 09:43:33]

This is how it was done in older IPC-based messaging for similar features (and
the new Mojo versions in this class). I'll try to figure out how to do it
without passing the origin and will get back to you. If I find a way, I will
also patch other methods in this class.

+      => (array<AudioInputDeviceCapabilities> audio_input_device_capabilities);
+
   // Creates a subscription for device-change notifications for the calling
   // frame/security origin. It is the responsibility of the caller to send
   // |subscription_id| values that are unique per device type.
   // Requests to create a subscription with an ID that already exists for type
   // |type| are invalid and result in a renderer crash.
   SubscribeDeviceChangeNotifications(MediaDeviceType type,
                                      uint32 subscription_id,
                                      url.mojom.Origin security_origin);
 
   // Removes a subscription to device-change notifications for the calling
   // frame. The caller is responsible for sending |subscription_id| values that
   // that refer to existing subscriptions for type |type|. Requests to remove
   // a nonexisting subscription with are invalid and result in a renderer crash.
   UnsubscribeDeviceChangeNotifications(MediaDeviceType type,
                                        uint32 subscription_id);
 };
 
 // This object lives in the renderer process and is used by the browser process
 // to pass device-change notifications to the renderer.
 interface MediaDevicesListener {
   // Called to notify a change in the set of devices of type |type| for
   // subscription |subscription_id|. |device_infos| contains the new list of
   // devices of type |type|, with device and group IDs obfuscated according to
   // the subscription's security origin.
   OnDevicesChanged(MediaDeviceType type,
                    uint32 subscription_id,
                    array<MediaDeviceInfo> device_infos);
 };