Add Polymer tests for cr-settings-prefs

chrome/test/data/webui/polymer_browser_test_base.js

 // Copyright 2015 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.
 
 /**
  * @fileoverview Framework for running JavaScript tests of Polymer elements.
  */
 
 /**
  * Test fixture for Polymer element testing.
@@ skipping 77 matching lines @@
  */
 PolymerTest.getLibraries = function(basePath) {
   // Ensure basePath ends in '/'.
   if (basePath.length && basePath[basePath.length - 1] != '/')
     basePath += '/';
 
   return PolymerTest.prototype.extraLibraries.map(function(library) {
     return basePath + library;
   });
 };
+
+/**
+ * Returns a promise which asynchronously calls |fn| and is also resolved
+ * asynchronously. Repeated calls to this function ensure each call waits for
+ * the previous promise to resolve, allowing any setTimeouts called by the prior
+ * function to be queued beforehand. For example:
+ *     PolymerTest.async(fn1); PolymerTest.async(fn2).then(success, failure);
+ * If fn1 calls setTimeout(asyncFn), fn2 won't be called until after asyncFn is
+ * called.
+ * @param {function()=} opt_fn
+ * @return {Promise}
+ */
+PolymerTest.async = function(opt_fn) {
+  PolymerTest.lastPromise_ = PolymerTest.lastPromise_.then(function() {
+    return new Promise(function(resolve) {
+      if (opt_fn)
+        setTimeout(opt_fn);
+      setTimeout(resolve);
+    });
+  });
+  return PolymerTest.lastPromise_;
+};
+
+/** @private {Promise} */
+PolymerTest.lastPromise_ = Promise.resolve();