Extracted UsbConfigDescriptor, UsbInterfaceDescriptor and helper classes

extensions/browser/api/usb/usb_apitest.cc

Index: extensions/browser/api/usb/usb_apitest.cc
diff --git a/extensions/browser/api/usb/usb_apitest.cc b/extensions/browser/api/usb/usb_apitest.cc
index 335258de1349ac24735eb00d5f44c1c3cc73e2e6..785031768a053688c78cb46d9358eee2b0b74eba 100644
--- a/extensions/browser/api/usb/usb_apitest.cc
+++ b/extensions/browser/api/usb/usb_apitest.cc
@@ -19,6 +19,7 @@ using usb_service::UsbConfigDescriptor;
 using usb_service::UsbDevice;
 using usb_service::UsbDeviceHandle;
 using usb_service::UsbEndpointDirection;
+using usb_service::UsbInterfaceDescriptor;
 using usb_service::UsbService;
 using usb_service::UsbTransferCallback;
 
@@ -93,6 +94,8 @@ class MockUsbDeviceHandle : public UsbDeviceHandle {
 class MockUsbConfigDescriptor : public UsbConfigDescriptor {
  public:
   MOCK_CONST_METHOD0(GetNumInterfaces, size_t());
+  MOCK_CONST_METHOD1(GetInterface,
+                     scoped_refptr<const UsbInterfaceDescriptor>(size_t index));
 
  protected:
   virtual ~MockUsbConfigDescriptor() {}