MD Settings: Remove usage of deprecated iron-flex-layout.html.

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

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/action_link.html">
 <link rel="import" href="chrome://resources/html/action_link_css.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.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="../route.html">
 <link rel="import" href="../settings_shared_css.html">
 <link rel="import" href="constants.html">
 <link rel="import" href="site_details_permission.html">
 <link rel="import" href="site_settings_behavior.html">
 <link rel="import" href="website_usage_private_api.html">
 
 <dom-module id="site-details">
   <template>
@@ skipping 26 matching lines @@
       </div>
       <div class="middle">[[site.displayName]]</div>
     </div>
     <template is="dom-if" if="[[storedData_]]">
       <div id="usage">
         <div class="settings-box first">
           <h2>$i18n{siteSettingsUsage}</h2>
         </div>
         <div class="list-frame">
           <div class="list-item" id="storage">
-            <div class="flex">[[storedData_]]</div>
+            <div class="start">[[storedData_]]</div>
             <paper-icon-button icon="cr:delete"
                 on-tap="onConfirmClearStorage_"
                 alt="$i18n{siteSettingsDelete}"></paper-icon-button>
           </div>
         </div>
       </div>
     </template>
     <div class="settings-box first">
       <h2>$i18n{siteSettingsPermissions}</h2>
     </div>
@@ skipping 52 matching lines @@
         </a>
       </div>
     </div>
     <website-usage-private-api id="usageApi"
         website-data-usage="{{storedData_}}"
         website-storage-type="{{storageType_}}">
     </website-usage-private-api>
   </template>
   <script src="site_details.js"></script>
 </dom-module>