Layout the NTP footer with flexboxes.

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 ac36b04194effc1388a8e3332aab22437d50c5f5..e4399d88f691975f6b516dfe93623ef0fa0107d7 100644
--- a/chrome/browser/resources/ntp4/other_sessions.js
+++ b/chrome/browser/resources/ntp4/other_sessions.js
@@ -247,7 +247,7 @@ cr.define('ntp', function() {
       }
 
       // The menu button is shown iff tab sync is enabled.
-      this.hidden = !isTabSyncEnabled;
+      this.classList.toggle('invisible', !isTabSyncEnabled);
     },
 
     /**
@@ -259,7 +259,7 @@ cr.define('ntp', function() {
       if (signedIn)
         chrome.send('getForeignSessions');
       else
-        this.hidden = true;
+        this.classList.add('invisible');
     },
   };