MD Settings: [further] robustify default zoom level handling

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/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_page/appearance_browser_proxy.html">
 <link rel="import" href="/controls/controlled_radio_button.html">
 <link rel="import" href="/controls/settings_dropdown_menu.html">
 <link rel="import" href="/controls/settings_input.html">
@@ skipping 133 matching lines @@
           </div>
           <button class="subpage-arrow" is="paper-icon-button-light"></button>
         </div>
         <div class="settings-box"
             hidden="[[!pageVisibility.pageZoom]]">
           <div class="start">$i18n{pageZoom}</div>
           <div class="md-select-wrapper">
             <select id="zoomLevel" class="md-select"
                 on-change="onZoomLevelChange_">
               <template is="dom-repeat" items="[[pageZoomLevels_]]">
-                <option value="[[item]]">[[formatZoom_(item)]]%</option>
+                <option value="[[item]]"
+                    selected$="[[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>