MD History: Update sign in state in data source

chrome/browser/resources/md_history/app.js

Index: chrome/browser/resources/md_history/app.js
diff --git a/chrome/browser/resources/md_history/app.js b/chrome/browser/resources/md_history/app.js
index 40b41e212c7d76e5d4366b2c01529d1df0f2a28f..730ff7e0f8df5ed2bc22725f490c70eadd30e955 100644
--- a/chrome/browser/resources/md_history/app.js
+++ b/chrome/browser/resources/md_history/app.js
@@ -22,7 +22,10 @@ cr.define('md_history', function() {
 Polymer({
   is: 'history-app',
 
-  behaviors: [Polymer.IronScrollTargetBehavior],
+  behaviors: [
+    Polymer.IronScrollTargetBehavior,
+    WebUIListenerBehavior,
+  ],
 
   properties: {
     // Used to display notices for profile sign-in status.
@@ -105,6 +108,12 @@ Polymer({
     document.addEventListener('command', this.onCommand_.bind(this));
   },
 
+  /** @override */
+  attached: function() {
+    this.addWebUIListener('sign-in-state-updated',
+                          this.updateSignInState.bind(this));
+  },
+
   onFirstRender: function() {
     setTimeout(function() {
       chrome.send(