MD Settings: disable the On Startup "OK" button with no site content

chrome/browser/resources/settings/on_startup_page/startup_urls_page.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.
 
 /**
  * @typedef {{
  *   'title': string,
  *   'tooltip': string,
  *   'url': string
  * }}
@@ skipping 20 matching lines @@
 
   properties: {
     /**
      * Preferences state.
      */
     prefs: {
       type: Object,
       notify: true,
     },
 
-    newUrl: {
+    /** @private {string} */
+    newUrl_: {
       type: String,
+      value: '',
     },
 
     /**
      * Pages to load upon browser startup.
      * @private {!Array<!StartupPageInfo>}
      */
     startupPages_: Array,
   },
 
   attached: function() {
     var self = this;
     cr.define('Settings', function() {
       return {
         updateStartupPages: function() {
           return self.updateStartupPages_.apply(self, arguments);
         },
       };
     });
     chrome.send('onStartupPrefsPageLoad');
   },
 
   /** @private */
   updateStartupPages_: function(startupPages) {
     this.startupPages_ = startupPages;
   },
 
   /** @private */
   onAddPageTap_: function() {
+    this.newUrl_ = '';
     this.$.addUrlDialog.open();
   },
 
   /** @private */
   onUseCurrentPagesTap_: function() {
     chrome.send('setStartupPagesToCurrentPages');
   },
 
   /** @private */
   onCancelTap_: function() {
     this.$.addUrlDialog.close();
   },
 
+  /**
+   * @return {boolean} Whether tapping the OK button should be allowed.
+   * @private
+   */
+  isOkAllowed_: function() {
+    return this.newUrl_.length > 0;

[dschuyler, 2016/03/01 03:15:52]

Can we re-add the trim() to avoid urls like ' ' and '   http://example.com'

[Dan Beam, 2016/03/02 19:56:42]

Done.

+  },
+
   /** @private */
   onOkTap_: function() {
-    var value = this.newUrl && this.newUrl.trim();
-    if (!value)
-      return;
-    chrome.send('addStartupPage', [value]);
-    this.newUrl = '';
+    assert(this.isOkAllowed_());
+    chrome.send('addStartupPage', [this.newUrl_]);
     this.$.addUrlDialog.close();
   },
 
   /**
    * @param {!{model: !{index: number}}} e
    * @private
    */
   onRemoveUrlTap_: function(e) {
     chrome.send('removeStartupPage', [e.model.index]);
   },
 });