Implement getConfiguration in WebUSBDeviceImpl.

device/devices_app/usb/public/interfaces/device.mojom

 // Copyright 2015 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 device.usb;
 
 enum OpenDeviceError {
   // Opening the device succeeded.
   OK,
 
@@ skipping 123 matching lines @@
   // The transfer succeeded, but the device sent less data than was requested.
   // This applies only to inbound transfers.
   SHORT_PACKET,
 };
 
 interface Device {
   // Retrieve a DeviceInfo struct containing metadata about the device,
   // including the set of all available device configurations.
   GetDeviceInfo() => (DeviceInfo? info);
 
-  // Retrieves the device's currently active configuration. May return null if
-  // the device is unconfigured.
-  GetConfiguration() => (ConfigurationInfo? info);
+  // Retrieves the |configuration_value| of the device's currently active
+  // configuration. Will return 0 if the device is unconfigured.
+  GetConfiguration() => (uint8 value);
 
   // Opens the device. Methods below require the device be opened first.
   Open() => (OpenDeviceError error);
 
   // Closes the device.
   Close() => ();
 
   // Initiates a device control transfer to set the device's configuration to
   // one with the configuration value |value|.
   SetConfiguration(uint8 value) => (bool success);
@@ skipping 105 matching lines @@
   // this transfer.
   //
   // |timeout| specifies the request timeout in milliseconds. A timeout of 0
   // indicates no timeout: the request will remain pending indefinitely until
   // completed or otherwise terminated.
   IsochronousTransferOut(uint8 endpoint_number,
                          array<array<uint8>> packets,
                          uint32 timeout)
       => (TransferStatus status);
 };