MD History: Show 'no synced tabs' when tab sync is disabled

chrome/browser/resources/md_history/synced_device_manager.js

 // Copyright 2016 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.
 
 /**
  * @typedef {{device: string,
  *           lastUpdateTime: string,
  *           separatorIndexes: !Array<number>,
  *           timestamp: number,
  *           tabs: !Array<!ForeignSessionTab>,
@@ skipping 171 matching lines @@
       }
     }
 
     // Then, append any new devices.
     for (var i = updateCount; i < sessionList.length; i++) {
       this.push('syncedDevices_', this.createInternalDevice_(sessionList[i]));
     }
   },
 
   /**
+   * End fetching synced tabs when sync is disabled.
+   */
+  tabSyncDisabled: function() {
+    this.fetchingSyncedTabs_ = false;

[tsergeant, 2016/08/08 04:49:15]

This doesn't quite work as intended in all cases:

If I am already signed in with the history page open, then open settings and
disable tab sync, then I would want the devices to disappear from the history
page.

The history page will receive a setForeignSessions message with
isTabSyncEnabled=false, but it won't change anything in the UI.

You could fix this by clearing the syncedDevices_ list here (
this.set('syncedDevices_', []) ), or by adding a new variable which controls
whether the list is shown.

[lshang, 2016/08/09 00:39:29]

Done. Thanks for reminding:P

+  },
+
+  /**
    * Get called when user's sign in state changes, this will affect UI of synced
    * tabs page. Sign in promo gets displayed when user is signed out, and
    * different messages are shown when there are no synced tabs.
    * @param {boolean} isUserSignedIn
    */
   updateSignInState: function(isUserSignedIn) {
     // If user's sign in state didn't change, then don't change message or
     // update UI.
     if (this.signInState_ == isUserSignedIn)
       return;
 
     this.signInState_ = isUserSignedIn;
 
     // User signed out, clear synced device list and show the sign in promo.
     if (!isUserSignedIn) {
       this.clearDisplayedSyncedDevices_();
       return;
     }
     // User signed in, show the loading message when querying for synced
     // devices.
     this.fetchingSyncedTabs_ = true;
   },
 
   searchTermChanged: function(searchTerm) {
     this.clearDisplayedSyncedDevices_();
     this.updateSyncedDevices(this.sessionList);
   }
 });