md-settings: Fix back navigation from /resetProfileSettings.

chrome/test/data/webui/test_util.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.
+
+/*
+ * Waits for queued up tasks to finish before proceeding. Inspired by:
+ * https://github.com/Polymer/web-component-tester/blob/master/browser/environment/helpers.js#L97
+ */
+function flush() {
+  Polymer.dom.flush();
+  // Promises have microtask timing, so we use setTimeout to explicity force a
+  // new task.
+  return new Promise(function(resolve, reject) {
+    window.setTimeout(resolve, 0);
+  });
+}