Use embedded sign in UI for inline sign in flow

chrome/browser/resources/gaia_auth/util.js

 // Copyright (c) 2012 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.
 
 function $(id) {
   return document.getElementById(id);
 }
 
 function getUrlSearchParams(search) {
   var params = {};
 
   if (search) {
     // Strips leading '?'
     search = search.substring(1);
     var pairs = search.split('&');
     for (var i = 0; i < pairs.length; ++i) {
       var pair = pairs[i].split('=');
       if (pair.length == 2) {
         params[pair[0]] = decodeURIComponent(pair[1]);
       } else {
         params[pair] = true;
       }
     }
   }
 
   return params;
 }
+
+/**
+ * Creates a new URL which is the old URL with a GET param of key=value.
+ * Copied from ui/webui/resources/js/util.js.
+ * @param {string} url The base URL. There is not sanity checking on the URL so
+ *     it must be passed in a proper format.
+ * @param {string} key The key of the param.
+ * @param {string} value The value of the param.
+ * @return {string} The new URL.
+ */
+function appendParam(url, key, value) {
+  var param = encodeURIComponent(key) + '=' + encodeURIComponent(value);
+
+  if (url.indexOf('?') == -1)
+    return url + '?' + param;
+  return url + '&' + param;
+}