Add webusb notification UI unit tests

device/usb/mock_usb_device.cc

Index: device/usb/mock_usb_device.cc
diff --git a/device/usb/mock_usb_device.cc b/device/usb/mock_usb_device.cc
index a2fd46d1e2df7b7906cd5089c53e1a0876f41678..bd7cb54dea7321aac633132591a276e0f3547ebf 100644
--- a/device/usb/mock_usb_device.cc
+++ b/device/usb/mock_usb_device.cc
@@ -24,6 +24,20 @@ MockUsbDevice::MockUsbDevice(uint16 vendor_id,
                 base::UTF8ToUTF16(serial_number)) {
 }
 
+MockUsbDevice::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)
+    : UsbDevice(vendor_id,
+                product_id,
+                base::UTF8ToUTF16(manufacturer_string),
+                base::UTF8ToUTF16(product_string),
+                base::UTF8ToUTF16(serial_number)) {
+  webusb_landing_page_ = webusb_landing_page;
+}
+
 MockUsbDevice::~MockUsbDevice() {
 }