Add a sign-in promo message to the Other Devices menu.

chrome/browser/resources/ntp4/other_sessions.js

Index: chrome/browser/resources/ntp4/other_sessions.js
diff --git a/chrome/browser/resources/ntp4/other_sessions.js b/chrome/browser/resources/ntp4/other_sessions.js
index ccd693d67b8f1385a813ace1e3733ac51e0199bf..9abd87550e3db175d6179bbfb693aa7a6e1c39ca 100644
--- a/chrome/browser/resources/ntp4/other_sessions.js
+++ b/chrome/browser/resources/ntp4/other_sessions.js
@@ -36,15 +36,25 @@ cr.define('ntp', function() {
                                  this.onContextMenu_.bind(this), true);
       document.body.appendChild(this.menu);
 
+      this.promoMessage_ = $('other-sessions-promo-template').cloneNode(true);
+      this.promoMessage_.removeAttribute('id');  // Prevent a duplicate id.
+
       this.sessions_ = [];
       this.anchorType = cr.ui.AnchorType.ABOVE;
       this.invertLeftRight = true;
 
-      chrome.send('getForeignSessions');
       this.recordUmaEvent_(HISTOGRAM_EVENT.INITIALIZED);
     },
 
     /**
+     * Initialize this element.
+     * @param {boolean} signedIn Is the current user signed in?
+     */
+    initialize: function(signedIn) {
+      this.updateSignInState(signedIn);
+    },
+
+    /**
      * Record an event in the UMA histogram.
      * @param {Number} eventId The id of the event to be recorded.
      */
@@ -76,6 +86,15 @@ cr.define('ntp', function() {
     },
 
     /**
+     * Reset the menu contents to the default state.
+     * @private
+     */
+    resetMenuContents_: function() {
+      this.menu.innerHTML = '';
+      this.menu.appendChild(this.promoMessage_);
+    },
+
+    /**
      * Create a custom click handler for a link, so that clicking on a link
      * restores the session (including back stack) rather than just opening
      * the URL.
@@ -122,35 +141,41 @@ cr.define('ntp', function() {
     },
 
     /**
-     * Create the UI for the promo and place it inside the menu.
-     * The promo is shown instead of foreign session data when tab sync is
-     * not enabled for a profile.
-     */
-    showPromo_: function() {
-      var message = localStrings.getString('otherSessionsEmpty');
-      this.menu.appendChild(this.ownerDocument.createTextNode(message));
-    },
-
-    /**
-     * Sets the menu model data.
+     * Sets the menu model data. An empty list means that either there are no
+     * foreign sessions, or tab sync is disabled for this profile.
+     * |isTabSyncEnabled| makes it possible to distinguish between the cases.
+     *
      * @param {Array} sessionList Array of objects describing the sessions
-     * from other devices.
+     *     from other devices.
+     * @param {boolean} isTabSyncEnabled Is tab sync enabled for this profile?
      */
-    set sessions(sessionList) {
-      // Clear the current contents of the menu.
-      this.menu.innerHTML = '';
-
-      // Rebuild the menu with the new data.
-      for (var i = 0; i < sessionList.length; i++) {
-        this.addSession_(sessionList[i]);
+    setForeignSessions: function(sessionList, isTabSyncEnabled) {
+      this.sessions_ = sessionList;
+      this.resetMenuContents_();
+      if (sessionList.length > 0) {
+        // Rebuild the menu with the new data.
+        for (var i = 0; i < sessionList.length; i++) {
+          this.addSession_(sessionList[i]);
+        }
       }
 
-      if (sessionList.length == 0)
-        this.classList.add('invisible');
-      else
+      // The menu button is shown iff tab sync is enabled.
+      if (isTabSyncEnabled)
         this.classList.remove('invisible');
+      else
+        this.classList.add('invisible');
+    },
 
-      this.sessions_ = sessionList;
+    /**
+     * Called when this element is initialized, and from the new tab page when
+     * the user's signed in state changes,
+     * @param {boolean} signedIn Is the user currently signed in?
+     */
+    updateSignInState: function(signedIn) {
+      if (signedIn)
+        chrome.send('getForeignSessions');
+      else
+        this.classList.add('invisible');
     },
   };