MD WebUI: change how initial focus works in <dialog>s now that they know about shadow DOM

ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html

 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/assert.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/default-theme.html">
 
 <dom-module id="cr-dialog">
   <template>
     <style>
       :host {
@@ skipping 15 matching lines @@
         position: fixed;
         right: 0;
         top: 0;
       }
 
       .title-container {
         align-items: center;
         border-bottom: 1px solid var(--divider-color);
         display: flex;
         min-height: 52px;
+        outline: none;
       }
 
       :host ::content .title {
         font-size: 123.07%; /* (16px / 13px) * 100 */
-        outline: none;
       }
 
       #close {
         --paper-icon-button: {
           height: 40px;
           width: 40px;
         };
         -webkit-margin-end: 6px;
         /* <paper-icon-button> overrides --iron-icon-{height,width}, so this
          * padding essentially reduces 40x40 to 20x20. */
@@ skipping 37 matching lines @@
         border-bottom-left-radius: inherit;
         border-bottom-right-radius: inherit;
         margin: 0;
         padding: 16px 20px;
       }
 
       :host ::content .border-top-divider {
         border-top: 1px solid var(--divider-color);
       }
     </style>
-    <div class="title-container">
+    <div class="title-container" tabindex="-1">
       <content select=".title"></content>
       <paper-icon-button icon="cr:clear" on-tap="cancel" id="close"
           aria-label$="[[closeText]]">
       </paper-icon-button>
     </div>
     <div class="body-container">
       <content select=".body"></content>
     </div>
     <content select=".button-container"></content>
     <content select=".footer"></content>
   </template>
   <script src="cr_dialog.js"></script>
 </dom-module>