Add Throbber control for DOMUI. Use it everywhere in options and in Sync setup UI.

chrome/browser/resources/options/import_data_overlay.html

 <div id="import-data-overlay" class="page hidden">
   <h1 i18n-content="importDataTitle"></h1>
   <div>
     <span i18n-content="importFromLabel"></span>
     <select id="import-browsers">
       <option i18n-content="importLoading"></option>
     </select>
   </div>
   <div id="import-checkboxes">
     <div i18n-content="importDescription"></div>
     <div>
       <input id="import-history" type="checkbox">
       <label for="import-history" i18n-content="importHistory"></label>
     </div>
     <div>
       <input id="import-favorites" type="checkbox">
       <label for="import-favorites" i18n-content="importFavorites"></label>
     </div>
     <div>
       <input id="import-passwords" type="checkbox">
       <label for="import-passwords" i18n-content="importPasswords"></label>
     </div>
     <div>
       <input id="import-search" type="checkbox">
       <label for="import-search" i18n-content="importSearch"></label>
     </div>
   </div>
   <div class="action-area">
-    <span id="import-throbber"></span>
+    <div id="import-throbber" class="throbber"></div>
     <div class="button-strip">
       <button id="import-data-cancel" i18n-content="cancel"></button>
       <button id="import-data-commit" i18n-content="importCommit"></button>
     </div>
   </div>
 </div>