Implement getConfiguration in WebUSBDeviceImpl.

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

Index: device/devices_app/usb/public/interfaces/device.mojom
diff --git a/device/devices_app/usb/public/interfaces/device.mojom b/device/devices_app/usb/public/interfaces/device.mojom
index a5e2905ed32948adef105abde36bb0c263c03259..45797b7495da39173097b03fe4d820665b3eaf40 100644
--- a/device/devices_app/usb/public/interfaces/device.mojom
+++ b/device/devices_app/usb/public/interfaces/device.mojom
@@ -141,9 +141,9 @@ interface 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);