Associate the instant label text with a specific checkbox.

chrome/browser/resources/options/browser_options.html

 <div id="browserPage" class="page" hidden>
   <h1 i18n-content="browserPage"></h1>
   <div class="displaytable">
     <section id="startupSection">
       <h3 i18n-content="startupGroupName"></h3>
       <div>
         <div class="radio">
           <label>
             <input type="radio" name="startup" value="0"
                 pref="session.restore_on_startup"
@@ skipping 79 matching lines @@
     </section>
     <section>
       <h3 i18n-content="defaultSearchGroupName"></h3>
         <div id="defaultSearchEngineGroup">
           <div>
             <select id="defaultSearchEngine" class="weakrtl"></select>
             <button id="defaultSearchManageEnginesButton"
                 i18n-content="defaultSearchManageEngines"></button>
           </div>
           <div id="instantOption" class="checkbox">
-            <label>
+            <label id="instantLabel">
               <!-- TODO(estade): metric? -->
               <input id="instantFieldTrialCheckbox" type="checkbox"
                   checked="checked" hidden>
               <input id="instantEnabledCheckbox" type="checkbox"
                   pref="instant.enabled">
               <span i18n-content="instantName"></span>
             </label>
           </div>
           <div class="suboption informational-text">
             <span i18n-content="instantWarningText"></span>
             <a target="_blank" i18n-values="href:instantLearnMoreLink"
                i18n-content="learnMore"></a>
           </div>
         </div>
     </section>
 <if expr="not pp_ifdef('chromeos')">
     <section>
       <h3 i18n-content="defaultBrowserGroupName"></h3>
       <div>
         <button id="defaultBrowserUseAsDefaultButton"
             i18n-content="defaultBrowserUseAsDefault"></button>
         <div id="defaultBrowserState"
             i18n-content="defaultBrowserUnknown"></div>
       </div>
     </section>
 </if>
   </div>
 </div>