Track USB device configuration state in Blink.

device/usb/usb_device.h

 // Copyright 2014 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.
 
 #ifndef DEVICE_USB_USB_DEVICE_H_
 #define DEVICE_USB_USB_DEVICE_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 57 matching lines @@
   // On ChromeOS the permission_broker service is used to change the ownership
   // of USB device nodes so that Chrome can open them. On other platforms these
   // functions are no-ops and always return true.
   virtual void CheckUsbAccess(const ResultCallback& callback);
 
   // Creates a UsbDeviceHandle for further manipulation.
   virtual void Open(const OpenCallback& callback) = 0;
 
   // Gets the UsbConfigDescriptor for the active device configuration or nullptr
   // if the device is unconfigured.
-  virtual const UsbConfigDescriptor* GetActiveConfiguration() = 0;
+  virtual const UsbConfigDescriptor* GetActiveConfiguration() const = 0;
 
   void AddObserver(Observer* observer);
   void RemoveObserver(Observer* observer);
 
  protected:
   friend class UsbService;
 
   UsbDevice(uint16_t vendor_id,
             uint16_t product_id,
             const base::string16& manufacturer_string,
@@ skipping 23 matching lines @@
   const uint16_t product_id_;
 
   base::ObserverList<Observer, true> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(UsbDevice);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_USB_USB_DEVICE_H_