MD Settings: minor cleanup of content settings code.

chrome/browser/resources/settings/site_settings/site_data.html

 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout-classes.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="../settings_page/settings_subpage_search.html">
 <link rel="import" href="../settings_shared_css.html">
 <link rel="import" href="cookie_tree_behavior.html">
@@ skipping 13 matching lines @@
       .remove-site {
         -webkit-margin-end: 0;
       }
 
       .subtitle-row {
         margin-top: 9px;  /* With 15px in sub-items == 24px total margin. */
       }
     </style>
     <div class="settings-box first subtitle-row">
       <div class="start">
-        <div>$i18n{siteSettingsCookieHeader}</div>
+        <h2>$i18n{siteSettingsCookieHeader}</h2>
       </div>
       <settings-subpage-search id="filter" on-search-changed="onSearchChanged_"
           label="$i18n{siteSettingsCookieSearch}">
       </settings-subpage-search>
     </div>
     <div class="settings-box continuation">
       <paper-button class="secondary-button" id="removeShowingSites"
           on-tap="onRemoveShowingSitesTap_"
           hidden$="[[!isRemoveButtonVisible_(sites, renderedItemCount)]]">
         [[computeRemoveLabel_(filterString_)]]
@@ skipping 34 matching lines @@
         <paper-button class="action-button" on-tap="onConfirmDelete_">
           $i18n{siteSettingsCookiesClearAll}
         </paper-button>
       </div>
     </dialog>
   </template>
   <script src="cookie_info.js"></script>
   <script src="cookie_tree_node.js"></script>
   <script src="site_data.js"></script>
 </dom-module>