Add chrome://usb-internals page for adding and removing test devices.

chrome/browser/ui/webui/usb_internals/usb_internals.mojom

+// Copyright 2016 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.
+
+module mojom;
+
+import "url/mojo/origin.mojom";
+import "url/mojo/url.mojom";
+
+struct TestDeviceInfo {
+  string guid;
+  string name;
+  string serial_number;
+  url.mojom.Url landing_page;
+  url.mojom.Origin allowed_origin;
+};
+
+interface UsbInternalsPageHandler {
+  // Simulate the connection of a new device with the given properties.
+  AddDeviceForTesting(string name,
+                      string serial_number,
+                      string landing_page,
+                      string allowed_origin) => (bool success, string message);
+
+  // Simulate the disconnection of a device added with the function above.
+  RemoveDeviceForTesting(string guid) => ();
+
+  // Retrieves the list of test devices added with this API.
+  GetTestDevices() => (array<TestDeviceInfo> devices);
+};