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

chrome/browser/resources/usb_internals/usb_internals.js

+// 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.
+
+/**
+ * Javascript for usb_internals.html, served from chrome://usb-internals/.
+ */
+
+(function() {
+  // Connection to the UsbInternalsPageHandler instance running in the browser
+  // process.
+  let pageHandler = null;
+
+  function refreshDeviceList() {
+    pageHandler.getTestDevices().then(function(response) {
+      let tableBody = $('test-device-list');
+      while (tableBody.firstChild)

[dpapad, 2016/08/05 17:25:11]

Nit: I think you can clear the tableBody element in an easier way as follows,

tableBody.innerHTML = '';

[Reilly Grant (use Gerrit), 2016/08/05 18:08:35]

Done.

+        tableBody.removeChild(tableBody.firstChild);
+      for (let device of response.devices) {
+        let row = document.createElement('tr');
+        let name = document.createElement('td');
+        let serialNumber = document.createElement('td');
+        let landingPage = document.createElement('td');
+        let allowedOrigin = document.createElement('td');
+        let remove = document.createElement('td');
+        let removeButton = document.createElement('button');
+        name.textContent = device.name;
+        serialNumber.textContent = device.serial_number;
+        landingPage.textContent = device.landing_page;
+        allowedOrigin.textContent = device.allowed_origin;
+        removeButton.addEventListener('click', function(e) {

[dpapad, 2016/08/05 17:25:11]

Nit: The |e| parameter is not used, so it can be omitted it.

[Reilly Grant (use Gerrit), 2016/08/05 18:08:35]

Done.

+          pageHandler.removeDeviceForTesting(device.guid)
+              .then(refreshDeviceList);
+        });
+        removeButton.textContent = 'Remove';
+        row.appendChild(name);
+        row.appendChild(serialNumber);
+        row.appendChild(landingPage);
+        row.appendChild(allowedOrigin);
+        remove.appendChild(removeButton);
+        row.appendChild(remove);
+        tableBody.appendChild(row);
+      }
+    });
+  }
+
+  function addTestDevice(event) {
+    pageHandler.addDeviceForTesting(
+        $('test-device-name').value,
+        $('test-device-serial').value,
+        $('test-device-landing-page').value,
+        $('test-device-allowed-origin').value).then(function(response) {
+      if (response.success)
+        refreshDeviceList();
+      $('add-test-device-result').textContent = response.message;
+      $('add-test-device-result').className =
+          response.success ? 'action-success' : 'action-failure';
+    });
+    event.preventDefault();
+  }
+
+  /**
+   * Helper to convert callback-based define() API to a promise-based API.
+   * @param {!Array<string>} moduleNames
+   * @return {!Promise}
+   */
+  function importModules(moduleNames) {
+    return new Promise(function(resolve, reject) {
+      define(moduleNames, function(var_args) {
+        resolve(Array.prototype.slice.call(arguments, 0));
+      });
+    });
+  }
+
+  function initializeProxies() {
+    return importModules([
+      'mojo/public/js/connection',
+      'chrome/browser/ui/webui/usb_internals/usb_internals.mojom',
+      'content/public/renderer/frame_interfaces',
+    ]).then(function(modules) {
+      let connection = modules[0];
+      let mojom = modules[1];
+      let frameInterfaces = modules[2];
+
+      pageHandler = connection.bindHandleToProxy(
+          frameInterfaces.getInterface(mojom.UsbInternalsPageHandler.name),
+          mojom.UsbInternalsPageHandler);
+    });
+  }
+
+  document.addEventListener('DOMContentLoaded', function() {
+    initializeProxies().then(function() {
+      $('add-test-device-form').addEventListener('submit', addTestDevice);
+      refreshDeviceList();
+    });
+  });
+})();