Add support for sending a USB SET_CONFIGURATION request.

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 "base/basictypes.h"
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
@@ skipping 33 matching lines @@
   // Creates a UsbDeviceHandle for further manipulation.
   // Blocking method. Must be called on FILE thread.
   virtual scoped_refptr<UsbDeviceHandle> Open() = 0;
 
   // Explicitly closes a device handle. This method will be automatically called
   // by the destructor of a UsbDeviceHandle as well.
   // Closing a closed handle is a safe
   // Blocking method. Must be called on FILE thread.
   virtual bool Close(scoped_refptr<UsbDeviceHandle> handle) = 0;
 
-  // Gets the UsbConfigDescriptor for the active device configuration.
+  // Gets the UsbConfigDescriptor for the active device configuration or nullptr
+  // if the device is unconfigured.
   // Blocking method. Must be called on FILE thread.
-  virtual const UsbConfigDescriptor& GetConfiguration() = 0;
+  virtual const UsbConfigDescriptor* GetConfiguration() = 0;
 
   // Gets the manufacturer string of the device, or returns false.
   // Blocking method. Must be called on FILE thread.
   // TODO(reillyg): Make this available from the UI thread. crbug.com/427985
   virtual bool GetManufacturer(base::string16* manufacturer) = 0;
 
   // Gets the product string of the device, or returns false.
   // Blocking method. Must be called on FILE thread.
   // TODO(reillyg): Make this available from the UI thread. crbug.com/427985
   virtual bool GetProduct(base::string16* product) = 0;
@@ skipping 20 matching lines @@
   const uint32 unique_id_;
 
   ObserverList<Observer> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(UsbDevice);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_USB_USB_DEVICE_H_