[Sync] Make SESSIONS an implicit type

chrome/browser/resources/sync_setup_overlay.html

 <div id="sync-setup-overlay" class="page" hidden>
   <div class="close-button"></div>
   <div id="sync-setup-login" hidden>
     <div id="promo-title-container" hidden>
       <h1 i18n-content="promoTitle"></h1>
       <h2>
         <span i18n-content="promoTitleShort"></span>
         <a id="promo-learn-more" i18n-content="promoLearnMore"
             i18n-values="href:promoLearnMoreURL">
         </a>
@@ skipping 217 matching lines @@
                       i18n-values="title:preferences"></span>
                 </label>
               </div>
               <div class="sync-type-checkbox checkbox">
                 <label>
                   <input id="themes-checkbox" type="checkbox">
                   <span i18n-content="themes" i18n-values="title:themes">
                   </span>
                 </label>
               </div>
-              <div id="sessions-item" class="sync-type-checkbox checkbox">
+              <div id="tabs-item" class="sync-type-checkbox checkbox">
                 <label>
-                  <input id="sessions-checkbox" type="checkbox">
+                  <input id="tabs-checkbox" type="checkbox">
                   <span i18n-content="openTabs" il8n-values="title:tabs">
                   </span>
                 </label>
               </div>
             </div>
           </div>
           <div class="sync-configuration-errors">
             <div id="error-text" i18n-content="syncZeroDataTypesError"
                 class="sync-configuration-error reset-hidden" hidden></div>
           </div>
@@ skipping 154 matching lines @@
       <span i18n-values=".innerHTML:stopSyncingExplanation"></span>
     </div>
     <div class="action-area button-strip">
       <input id="stop-syncing-cancel" type="button"
           i18n-values="value:cancel">
       <input id="stop-syncing-ok" type="button"
           i18n-values="value:stopSyncingConfirm">
     </div>
   </div>
 </div>