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

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="../controls/controlled_radio_button.html">
 <link rel="import" href="../controls/extension_controlled_indicator.html">
 <link rel="import" href="../controls/settings_radio_group.html">
 <link rel="import" href="on_startup_browser_proxy.html">
 <link rel="import" href="startup_urls_page.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="settings-on-startup-page">
   <template>
-    <style include="settings-shared"></style>
+    <style include="settings-shared">
+      .block {
+        display: block;
+      }
+    </style>
     <div class="settings-box block first">
       <settings-radio-group id="onStartupRadioGroup"
           pref="{{prefs.session.restore_on_startup}}">
         <controlled-radio-button name="[[prefValues_.OPEN_NEW_TAB]]"
             pref="[[prefs.session.restore_on_startup]]"
             label="$i18n{onStartupOpenNewTab}"
             no-extension-indicator>
         </controlled-radio-button>
         <template is="dom-if" if="[[showIndicator_(
             ntpExtension_, prefs.session.restore_on_startup.value)]]">
@@ skipping 15 matching lines @@
       </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>
     </template>
   </template>
   <script src="on_startup_page.js"></script>
 </dom-module>