MD Settings: On Startup, extract dialog to its own file.

chrome/browser/resources/settings/on_startup_page/on_startup_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/paper-radio-button/paper-radio-button.html">
 <link rel="import" href="chrome://md-settings/controls/settings_radio_group.html">
 <link rel="import" href="chrome://md-settings/on_startup_page/startup_urls_page.html">
 <link rel="import" href="chrome://md-settings/settings_shared_css.html">
 
 <dom-module id="settings-on-startup-page">
   <link rel="import" type="css" href="on_startup_shared.css">
   <template>
     <style include="settings-shared"></style>
     <div class="settings-box block first">
       <settings-radio-group id="onStartupRadioGroup"
           pref="{{prefs.session.restore_on_startup}}">
         <paper-radio-button name="[[prefValues_.OPEN_NEW_TAB]]">
           $i18n{onStartupOpenNewTab}
         </paper-radio-button>
         <paper-radio-button name="[[prefValues_.CONTINUE]]">
           $i18n{onStartupContinue}
         </paper-radio-button>
         <paper-radio-button name="[[prefValues_.OPEN_SPECIFIC]]">
           $i18n{onStartupOpenSpecific}
         </paper-radio-button>
       </settings-radio-group>
     </div>
     <template is="dom-if"
         if="[[showStartupUrls_(prefs.session.restore_on_startup.value)]]">
-      <settings-startup-urls-page prefs="{{prefs}}">
-      </settings-startup-urls-page>
+      <settings-startup-urls-page></settings-startup-urls-page>
     </template>
   </template>
   <script src="on_startup_page.js"></script>
 </dom-module>