MD Settings: Close edit startup URL dialog, if underlying URL list changes.

chrome/browser/resources/settings/on_startup_page/startup_urls_page.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
+<link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_scrollable_behavior.html">
 <link rel="import" href="/settings_shared_css.html">
 <link rel="import" href="/on_startup_page/startup_url_dialog.html">
 <link rel="import" href="/on_startup_page/startup_url_entry.html">
 <link rel="import" href="/on_startup_page/startup_urls_page_browser_proxy.html">
 
 <dom-module id="settings-startup-urls-page">
   <template>
     <style include="settings-shared">
@@ skipping 15 matching lines @@
           </template>
         </iron-list>
       </div>
       <div class="list-item list-button" id="addPage" on-tap="onAddPageTap_">
         $i18n{onStartupAddNewPage}
       </div>
       <div class="list-item list-button" id="useCurrentPages"
           on-tap="onUseCurrentPagesTap_">$i18n{onStartupUseCurrent}</div>
     </div>
     <template is="dom-if" if="[[showStartupUrlDialog_]]" restamp>
-      <settings-startup-url-dialog model="[[startupUrlDialogModel_]]">
+      <settings-startup-url-dialog model="[[startupUrlDialogModel_]]"
+          on-close="destroyUrlDialog_">
       </settings-startup-url-dialog>
     </template>
   </template>
   <script src="startup_urls_page.js"></script>
 </dom-module>