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

content/common/media/media_devices.mojom

Index: content/common/media/media_devices.mojom
diff --git a/content/common/media/media_devices.mojom b/content/common/media/media_devices.mojom
index 93e943225af7e7d8a2a85ef8b9881283805dd712..339c30aed8168d0f67c1474f59c4104de63d975d 100644
--- a/content/common/media/media_devices.mojom
+++ b/content/common/media/media_devices.mojom
@@ -5,6 +5,7 @@
 module mojom;
 
 import "media/capture/mojo/video_capture_types.mojom";
+import "media/mojo/interfaces/audio_parameters.mojom";
 import "url/mojo/origin.mojom";
 
 [Native]
@@ -31,6 +32,11 @@ struct VideoInputDeviceCapabilities {
   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.
@@ -43,15 +49,26 @@ interface MediaDevicesDispatcherHost {
                    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.