WebUI: For cr-dialog, handle Enter keys in paper-inputs.

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

 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="startup_urls_page_browser_proxy.html">
 
 <dom-module id="settings-startup-url-dialog">
   <template>
     <style include="settings-shared"></style>
     <dialog is="cr-dialog" id="dialog" close-text="$i18n{close}">
       <div class="title">[[dialogTitle_]]</div>
       <div class="body">
         <paper-input always-float-label id="url" label="$i18n{onStartupSiteUrl}"
-            value="{{url_}}" on-input="validate_" on-keypress="onKeypress_"
-            autofocus>
+            value="{{url_}}" on-input="validate_" autofocus>
         </paper-input>
       </div>
       <div class="button-container">
         <div class="action-buttons">
           <paper-button class="cancel-button" on-tap="onCancelTap_"
               id="cancel">$i18n{cancel}</paper-button>
           <paper-button id="actionButton" class="action-button"
               on-tap="onActionButtonTap_">[[actionButtonText_]]</paper-button>
         </div>
       </div>
     </dialog>
   </template>
   <script src="startup_url_dialog.js"></script>
 </dom-module>