Add IPC to query capabilities of video input devices.

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 "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 UNKNOWN, which would map to the empty string in
+// JavaScript.
+enum FacingMode {
+  USER,
+  ENVIRONMENT,
+  LEFT,
+  RIGHT,
+  UNKNOWN

[hta - Chromium, 2017/01/27 10:40:47]

Is there a particular reason for not calling it NONE and putting it first? This
just seems like a departure from existing patterns.

[Guido Urdaneta, 2017/01/27 14:10:47]

Changed to NONE. Wasn't aware of the pattern.

+};
+
+struct VideoInputDeviceCapabilities {
+  string device_id;
+  array<media.mojom.VideoCaptureFormat> formats;
+  FacingMode facing_mode;
+};
+
 // 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.
+  GetVideoInputCapabilities(url.mojom.Origin security_origin)
+      => (array<VideoInputDeviceCapabilities> video_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);
 };