MD History: add sign in promo in synced tabs when user isn't logged in

chrome/browser/resources/md_history/history.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Send the history query immediately. This allows the query to process during
 // the initial page startup.
 chrome.send('queryHistory', ['', 0, 0, 0, RESULTS_PER_PAGE]);
 chrome.send('getForeignSessions');
 
 /**
@@ skipping 55 matching lines @@
     /** @type {HistoryAppElement} */(appElem)
         .setForeignSessions(sessionList, isTabSyncEnabled);
   });
 }
 
 /**
  * Called when the history is deleted by someone else.
  */
 function historyDeleted() {
 }
+
+/**
+ * Called by the history backend after user's sign in state changes.
+ * @param {boolean} isUserSignedIn Whether user is signed in or not now.
+ */
+function updateSignInState(isUserSignedIn) {
+  var appElem = $('history-app');
+  waitForUpgrade(appElem).then(function() {
+    /** @type {HistoryAppElement} */(appElem)
+        .updateSignInState(isUserSignedIn);
+  });
+}