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

chrome/browser/resources/md_history/synced_device_manager.js

Index: chrome/browser/resources/md_history/synced_device_manager.js
diff --git a/chrome/browser/resources/md_history/synced_device_manager.js b/chrome/browser/resources/md_history/synced_device_manager.js
index 433fb7f88a5487479147853bbbf669a99f3ef12d..2f67292cf3167c7089617ed4c8ba65463b7ae636 100644
--- a/chrome/browser/resources/md_history/synced_device_manager.js
+++ b/chrome/browser/resources/md_history/synced_device_manager.js
@@ -189,6 +189,13 @@ Polymer({
   },
 
   /**
+   * 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.