Use dom-if to hide settings pages and show explicitly.

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

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/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/neon-animation/neon-animatable.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_page/settings_animated_pages.html">
 <link rel="import" href="chrome://md-settings/settings_page/settings_subheader.html">
 
 <dom-module id="settings-on-startup-page">
   <link rel="import" type="css"
       href="chrome://md-settings/settings_shared.css">
   <link rel="import" type="css" href="on_startup_shared.css">
   <template>
     <settings-animated-pages id="pages" current-route="{{currentRoute}}"
-        section="on-startup">
+        section="onStartup">

[Dan Beam, 2015/12/08 02:55:27]

please try to stop writing these: https://en.wikipedia.org/wiki/Omnibus_bill

[stevenjb, 2015/12/08 20:07:37]

https://codereview.chromium.org/1505113005

       <neon-animatable id="main">
         <div class="settings-box">
           <div id="locationLabel" i18n-content="onStartup"></div>
           <settings-radio-group pref="{{prefs.session.restore_on_startup}}">
             <paper-radio-button name="[[prefValues_.OPEN_NEW_TAB]]"
                 i18n-content="onStartupOpenNewTab">
             </paper-radio-button>
             <paper-radio-button name="[[prefValues_.CONTINUE]]"
                 i18n-content="onStartupContinue">
             </paper-radio-button>
@@ skipping 11 matching lines @@
       <neon-animatable id="startup-urls">
         <settings-subheader i18n-values="page-title:onStartupSetPages">
         </settings-subheader>
         <settings-startup-urls-page prefs="{{prefs}}">
         </settings-startup-urls-page>
       </neon-animatable>
     </settings-animated-pages>
   </template>
   <script src="on_startup_page.js"></script>
 </dom-module>