[Media Router] Show user email in header if cloud sink is present.

chrome/browser/resources/media_router/elements/media_router_header/media_router_header.html

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/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-toolbar/paper-toolbar.html">
 <dom-module name="media-router-header">
   <link rel="import" type="css" href="../../media_router_common.css">
   <link rel="import" type="css" href="media_router_header.css">
   <template>
-    <paper-toolbar class$="[[view]]">
+    <paper-toolbar id="header-toolbar" class$="[[view]]">
       <div id="back-button-container">
         <paper-icon-button id="back-button" icon="[[arrowDropIcon_]]"
             on-click="onBackButtonClick_"
             hidden$="[[computeBackButtonHidden_(view)]]">
         </paper-icon-button>
       </div>
       <div id="header-and-arrow-container" on-click="onHeaderOrArrowClick_">
         <span id="header-text" title="[[tooltip]]">
             [[headingText]]</span>
         <div id="arrow-drop-container">
           <paper-icon-button icon="[[computeArrowDropIcon_(view)]]"
               id="arrow-drop-icon" disabled$="[[arrowDropIconDisabled]]"
               hidden$="[[computeArrowDropIconHidden_(view)]]">
           </paper-icon-button>
         </div>
       </div>
       <div id="close-button-container">
         <paper-icon-button icon="close" id="close-button"
             on-click="onCloseButtonClick_">
         </paper-icon-button>
       </div>
+      <template is="dom-if" if="[[showEmail]]">
+        <div id="user-email-container" class="bottom fit">
+          <span>[[userEmail]]</span>
+        </div>
+      </template>
     </paper-toolbar>
   </template>
 <script src="media_router_header.js"></script>
 </dom-module>