MD Settings: Fix subpage visibility and add appearance page tests

chrome/browser/resources/settings/downloads_page/downloads_page.html

 <link rel="import" href="chrome://resources/html/util.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="../controls/controlled_button.html">
 <link rel="import" href="../controls/settings_toggle_button.html">
 <link rel="import" href="../settings_shared_css.html">
 <link rel="import" href="downloads_browser_proxy.html">
 
 <dom-module id="settings-downloads-page">
   <template>
@@ skipping 24 matching lines @@
     </div>
     <div class="settings-box block">
       <settings-toggle-button
           pref="{{prefs.download.prompt_for_download}}"
           label="$i18n{promptForDownload}">
       </settings-toggle-button>
 <if expr="chromeos">
       <settings-toggle-button
           pref="{{prefs.gdata.disabled}}"
           label="$i18n{disconnectGoogleDriveAccount}"
-          hidden="[[!pageVisibility.googleDrive]]">
+          hidden="[[!showPage_(pageVisibility.googleDrive)]]">
       </settings-toggle-button>
 </if>
     </div>
     <template is="dom-if" if="[[autoOpenDownloads_]]" restamp>
       <div class="settings-box">
         <div class="start">
           $i18n{openFileTypesAutomatically}
         </div>
         <div class="separator"></div>
         <paper-button id="resetAutoOpenFileTypes" class="secondary-button"
             on-tap="onClearAutoOpenFileTypesTap_">
           $i18n{clear}
         </paper-button>
       </div>
     </template>
   </template>
   <script src="downloads_page.js"></script>
 </dom-module>