MD Settings: Fix subpage visibility and add appearance page tests

chrome/browser/resources/settings/downloads_page/downloads_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.
 
 /**
  * @fileoverview
  * 'settings-downloads-page' is the settings page containing downloads
  * settings.
  *
  * Example:
@@ skipping 38 matching lines @@
   attached: function() {
     this.browserProxy_ = settings.DownloadsBrowserProxyImpl.getInstance();
 
     this.addWebUIListener('auto-open-downloads-changed', function(autoOpen) {
       this.autoOpenDownloads_ = autoOpen;
     }.bind(this));
 
     this.browserProxy_.initializeDownloads();
   },
 
+  /**
+   * @param {boolean|undefined} visibility
+   * @return {boolean}
+   * @private
+   */
+  showPage_: function(visibility) {
+    return visibility !== false;
+  },
+
   /** @private */
   selectDownloadLocation_: function() {
     listenOnce(this, 'transitionend', function() {
       this.browserProxy_.selectDownloadLocation();
     }.bind(this));
   },
 
   // <if expr="chromeos">
   /**
    * @param {string} path
@@ skipping 11 matching lines @@
     path = path.replace(/\//g, ' \u203a ');
     return path;
   },
   // </if>
 
   /** @private */
   onClearAutoOpenFileTypesTap_: function() {
     this.browserProxy_.resetAutoOpenFileTypes();
   },
 });