Add new instant extended specific pref.

chrome/browser/resources/options/browser_options.html

 <div id="settings" class="page" hidden>
   <header>
     <h1 i18n-content="settingsTitle"></h1>
   </header>
 <if expr="not pp_ifdef('chromeos')">
   <include src="sync_section.html">
 </if>
 <if expr="pp_ifdef('chromeos')">
   <section>
     <h3 i18n-content="sectionTitleInternet"></h3>
@@ skipping 128 matching lines @@
               pref="default_search_provider.enabled">
           </span>
           <button id="manage-default-search-engines"
               i18n-content="defaultSearchManageEngines">
           </button>
         </div>
         <div class="checkbox" guest-visibility="disabled">
           <span class="controlled-setting-with-label">
             <!-- TODO(estade): metric? -->
             <input id="instant-enabled-control" type="checkbox"
                 pref="instant.enabled" dialog-pref>

[Evan Stade, 2012/12/07 22:06:24]

I think you could do i18n-values="pref:someVariableName"

and make sure that loadTimeData has someVariableName set to either
instant.enabled or instant_extended.enabled

[MAD, 2012/12/08 15:53:11]

Done.

+            <!-- See the initializePage method comments for why we have two
+                 checkboxes that can be alternatively hidden !-->
+            <input id="instant-extended-enabled-control" type="checkbox"
+                pref="instant_extended.enabled" hidden>
             <span>
               <!-- TODO(estade) There's a link in here which should not be
                    inside a <label>. -->
               <label for="instant-enabled-control"
+                  id="instant-enabled-control-label"
                   i18n-values=".innerHTML:instantPrefAndWarning">
               </label>
               <span id="instant-enabled-indicator"
                   class="controlled-setting-indicator" pref="instant.enabled"
                   dialog-pref>
               </span>
             </span>
           </span>
         </div>
       </div>
@@ skipping 526 matching lines @@
   </section>
 </if>
 </div>  <!-- advanced-settings-container -->
 </div>  <!-- advanced-settings -->
 <footer>
   <button id="advanced-settings-expander" class="link-button"
       i18n-content="showAdvancedSettings">
   </button>
 </footer>
 </div>