[MD settings] minor changes to make OnStartup elements line up better

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

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-item/paper-icon-item.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-material/paper-material.html">
 
 <dom-module id="cr-settings-startup-urls-page">
   <link rel="import" type="css" href="chrome://md-settings/settings_page/settings_page.css">
   <link rel="import" type="css" href="on_startup_shared.css">
   <template>
     <div>
       <div class="entries">
         <template is="dom-repeat" items="{{prefs.session.startup_urls.value}}">
           <paper-icon-item>
             <iron-icon icon="image:brightness-1" item-icon></iron-icon>
             <span class="flex">[[item]]</span>
             <iron-icon on-tap="onRemoveUrlTap_" icon="clear">
             </iron-icon>
           </paper-icon-item>
         </template>
       </div>
-      <div class="horizontal layout center">
+      <paper-icon-item>
         <div i18n-content="onStartupAddPage"></div>&nbsp;
         <paper-input class="flex" no-label-float
             i18n-values="label:onStartupEnterUrl" value="{{newUrl}}">
         </paper-input>
-      </div>
-      <div class="horizontal layout">
+      </paper-icon-item>
+      <div class="button-row">
         <div class="flex">
           <paper-button on-tap="onUseCurrentPagesTap_"
               i18n-content="onStartupUseCurrent">
           </paper-button>
         </div>
         <paper-button on-tap="onCancelTap_" i18n-content="cancelButton">
         </paper-button>
         <paper-button on-tap="onOkTap_" raised i18n-content="okButton">
         </paper-button>
       </div>
     </div>
   </template>
   <script src="startup_urls_page.js"></script>
 </dom-module>