Migrate <cr-dialog> from PaperDialogBehavior to native <dialog>.

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

 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-a11y-keys/iron-a11y-keys.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="/i18n_setup.html">
 <link rel="import" href="/settings_shared_css.html">
 <link rel="import" href="/site_settings/constants.html">
 <link rel="import" href="/site_settings/site_settings_behavior.html">
 
 <dom-module id="add-site-dialog">
   <template>
     <style include="settings-shared"></style>
-    <cr-dialog id="dialog">
+    <dialog is="cr-dialog" id="dialog">
       <div class="title">$i18n{addSiteHeader}</div>
       <div class="body">
         <span class="start">$i18n{addSite}</span>
         <iron-a11y-keys id="keys" keys="enter"
             on-keys-pressed="onSubmit_"></iron-a11y-keys>
         <paper-input type="text" id="site" autofocus
             value="{{site_}}" on-input="validate_"></paper-input>
       </div>
       <div class="button-container">
         <paper-button class="cancel-button" dialog-dismiss>
             $i18n{cancel}
         </paper-button>
         <paper-button class="action-button" id="add"
             on-tap="onSubmit_" disabled>
           $i18n{add}
         </paper-button>
       </div>
-    </cr-dialog>
+    </dialog>
   </template>
   <script src="add_site_dialog.js"></script>
 </dom-module>