[MD settings] observe changes to default font size in Appearance

chrome/browser/resources/settings/appearance_page/appearance_page.html

 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/md_select_css.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="appearance_browser_proxy.html">
 <link rel="import" href="../controls/controlled_radio_button.html">
 <link rel="import" href="../controls/extension_controlled_indicator.html">
@@ skipping 155 matching lines @@
           </settings-dropdown-menu>
         </div>
         <div id="customize-fonts-subpage-trigger" class="settings-box"
             on-tap="onCustomizeFontsTap_" actionable>
           <div class="start">
             $i18n{customizeFonts}
           </div>
           <button class="subpage-arrow" is="paper-icon-button-light"
               aria-label="$i18n{customizeFonts}"></button>
         </div>
-        <div class="settings-box"
-            hidden="[[!pageVisibility.pageZoom]]">
+        <div class="settings-box" hidden="[[!pageVisibility.pageZoom]]">
           <div id="pageZoom" class="start">$i18n{pageZoom}</div>
           <div class="md-select-wrapper">
             <select id="zoomLevel" class="md-select" aria-labelledy="pageZoom"
                 on-change="onZoomLevelChange_">
               <template is="dom-repeat" items="[[pageZoomLevels_]]">
                 <option value="[[item]]"
                     selected="[[zoomValuesEqual_(item, defaultZoom_)]]">
                   [[formatZoom_(item)]]%
                 </option>
               </template>
             </select>
             <span class="md-select-underline"></span>
           </div>
         </div>
       </neon-animatable>
       <template is="dom-if" route-path="/fonts">
         <settings-subpage
             associated-control="[[$$('#customize-fonts-subpage-trigger')]]"
             page-title="$i18n{customizeFonts}">
           <settings-appearance-fonts-page prefs="{{prefs}}">
           </settings-appearance-fonts-page>
         </settings-subpage>
       </template>
     </settings-animated-pages>
   </template>
   <script src="appearance_page.js"></script>
 </dom-module>