[uber page] Split out part of headers CL to make review easier.

chrome/browser/resources/options2/browser_options.html

 <div id="browserPage" class="page" hidden>
   <span id="browser-options-search-field-container"
       class="search-field-container">
     <input id="search-field" type="search"
         i18n-values="placeholder:searchPlaceholder;aria-label:searchPlaceholder"
         incremental>
   </span>
-  <h1 i18n-content="browserPage"></h1>
+  <header><h1 i18n-content="browserPage"></h1></header>
 <if expr="not pp_ifdef('chromeos')">
   <section id="sync-section">
     <h3 i18n-content="sectionTitleSync"></h3>
     <div id="sync-overview" class="section-description" hidden>
       <p i18n-content="syncOverview"></p>
       <a i18n-values="href:syncLearnMoreURL" i18n-content="learnMore"></a>
     </div>
     <div id="sync-status" hidden>
       <span id="sync-status-text"></span>
       <button id="sync-action-link" class="link-button"></button>
@@ skipping 271 matching lines @@
   </section>
 </if>
   <section>
     <h3 i18n-content="sectionTitleAdvanced"></h3>
     <div>
       <button id="advancedOptionsButton"
           i18n-content="advancedOptionsButtonTitle"></button>
     </div>
   </section>
 </div>