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

chrome/browser/resources/settings/people_page/password_prompt_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="lock_screen_constants.html">
 <link rel="import" href="../settings_shared_css.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="settings-password-prompt-dialog">
   <template>
@@ skipping 11 matching lines @@
         close-text="$i18n{close}">
       <div class="title">$i18n{passwordPromptTitle}</div>
       <div class="body">
 
         <div class="settings-box first">$i18n{passwordPromptEnterPassword}</div>
 
         <paper-input id="passwordInput" type="password" autofocus
                      label="$i18n{passwordPromptPasswordLabel}"
                      no-label-float
                      value="{{password_}}"
-                     on-keydown="onKeydown_"
                      invalid$="[[passwordInvalid_]]"
                      error-message="$i18n{passwordPromptInvalidPassword}"
                      aria-disabled="false">
         </paper-input>
 
         <div class="button-strip">
           <paper-button class="cancel-button" on-tap="onCancelTap_">
             $i18n{cancel}
           </paper-button>
 
           <paper-button class="action-button" on-tap="submitPassword_"
                         disabled$="[[!enableConfirm_(password_,
                                                      passwordInvalid_)]]">
             $i18n{confirm}
           </paper-button>
         </div>
       </div>
     </dialog>
   </template>
   <script src="password_prompt_dialog.js"></script>
 </dom-module>