md-settings: wrap lock screen dialogs in dom-if.

chrome/browser/resources/settings/people_page/setup_pin_dialog.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 
 <link rel="import" href="chrome://resources/html/assert.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="../icons.html">
 <link rel="import" href="lock_screen_constants.html">
 <link rel="import" href="pin_keyboard.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="settings-setup-pin-dialog">
   <template>
     <style include="settings-shared">
       .error {
         color: var(--paper-red-500);
+        color: blue;
       }
 
       .error > iron-icon {
         --iron-icon-fill-color: var(--paper-red-500);
       }
 
       .warning {
         color: var(--paper-grey-700);
       }
 
@@ skipping 11 matching lines @@
     </style>
 
     <dialog is="cr-dialog" id="dialog" on-close="close"
         close-text="$i18n{close}">
       <div class="title">[[getTitleMessage_(isConfirmStep_)]]</div>
       <div class="body">
         <!-- Pin keyboard -->
         <div id="pinKeyboardDiv" class="settings-box continuation">
           <pin-keyboard id="pinKeyboard" on-pin-change="onPinChange_"
               on-submit="onPinSubmit_" value="{{pinKeyboardValue_}}"
-              has-error$="[[hasError_(problemMessage_, problemClass_)]]">
+              has-error$="[[hasError_(problemMessage_, problemClass_)]]"
+              autofocus>
             <!-- Warning/error; only shown if title is hidden. -->
             <div id="problemDiv" class$="[[problemClass_]]"
                 hidden$="[[!problemMessage_]]" problem>
               <iron-icon icon="settings:error-outline"></iron-icon>
               <span id="problemMessage">[[problemMessage_]]</span>
             </div>
           </pin-keyboard>
         </div>
       </div>
       <div class="button-container">
         <paper-button class="cancel-button" on-tap="onCancelTap_">
           $i18n{cancel}
         </paper-button>
 
         <paper-button class="action-button" on-tap="onPinSubmit_"
             disabled$="[[!enableSubmit_]]">
           <span>[[getContinueMessage_(isConfirmStep_)]]</span>
         </paper-button>
       </div>
     </dialog>
   </template>
 
   <script src="setup_pin_dialog.js"></script>
 </dom-module>