MD Settings: Fix subpage visibility and add appearance page tests

chrome/browser/resources/settings/appearance_page/appearance_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.
 
 
 /**
  * This is the absolute difference maintained between standard and
  * fixed-width font sizes. http://crbug.com/91922.
  * @const @private {number}
  */
@@ skipping 126 matching lines @@
   ready: function() {
     this.$.defaultFontSize.menuOptions = this.fontSizeOptions_;
     // TODO(dschuyler): Look into adding a listener for the
     // default zoom percent.
     this.browserProxy_.getDefaultZoom().then(function(zoom) {
       this.defaultZoom_ = zoom;
     }.bind(this));
   },
 
   /**
+   * @param {boolean|undefined} visibility
+   * @return {boolean}
+   * @private
+   */
+  showPage_: function(visibility) {
+    return visibility !== false;
+  },
+
+  /**
    * @param {number} zoom
    * @return {number} A zoom easier read by users.
    * @private
    */
   formatZoom_: function(zoom) {
     return Math.round(zoom * 100);
   },
 
   /**
    * @param {boolean} showHomepage Whether to show home page.
@@ skipping 149 matching lines @@
    * @see content::ZoomValuesEqual().
    * @param {number} zoom1
    * @param {number} zoom2
    * @return {boolean}
    * @private
    */
   zoomValuesEqual_: function(zoom1, zoom2) {
     return Math.abs(zoom1 - zoom2) <= 0.001;
   },
 });