Add webusb notification UI unit tests

device/usb/mock_usb_device.h

Index: device/usb/mock_usb_device.h
diff --git a/device/usb/mock_usb_device.h b/device/usb/mock_usb_device.h
index a60af2469904b3924581e3093f37d5edff2cc7bf..30b5bdd3b7b7e29f0a54d361e99228c11d87d0b0 100644
--- a/device/usb/mock_usb_device.h
+++ b/device/usb/mock_usb_device.h
@@ -22,6 +22,12 @@ class MockUsbDevice : public UsbDevice {
                 const std::string& manufacturer_string,
                 const std::string& product_string,
                 const std::string& serial_number);
+  MockUsbDevice(uint16 vendor_id,
+                uint16 product_id,
+                const std::string& manufacturer_string,
+                const std::string& product_string,
+                const std::string& serial_number,
+                const GURL& webusb_landing_page);
 
   MOCK_METHOD1(Open, void(const OpenCallback&));
   MOCK_METHOD1(Close, bool(scoped_refptr<UsbDeviceHandle>));