MD Settings: Fix case where 'REMOVE ALL SHOWN' button is erroneously shown.

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 28 matching lines @@
     </div>
     <div class="settings-box continuation">
       <paper-button class="secondary-button" id="removeShowingSites"
           on-tap="onRemoveShowingSitesTap_"
           hidden$="[[!isRemoveButtonVisible_(sites, renderedItemCount)]]">
         [[computeRemoveLabel_(filterString_)]]
       </paper-button>
     </div>
     <div class="list-frame vertical-list">
       <template is="dom-repeat" id="list" items="[[sites]]" filter="showItem_"
-          rendered-item-count="{{renderedItemCount}}">
+          rendered-item-count="{{renderedItemCount::dom-change}}"

[dschuyler, 2017/03/28 19:18:23]

Will this trigger/update more often than it did before, and/or is that likely to
be an issue? My concern is that dom-change may be spammy and this may slow
things down. If it's the same or better (or if there is no feasible alternative)
then this would be ok.

+          notify-dom-change>
         <div class="list-item two-line" on-tap="onSiteTap_" actionable>
           <div class="favicon-image" style$="[[computeSiteIcon(item.site)]]">
           </div>
           <div class="middle">
             [[item.site]]
             <div class="secondary" id="siteSecondary">[[item.localData]]</div>
           </div>
           <button class="subpage-arrow" is="paper-icon-button-light"
               aria-label$="[[item.site]]"
               aria-describedby="siteSecondary"></button>
@@ skipping 19 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>