RootWindowController::GetFullscreenWindow() should return the active one.

chrome/browser/fullscreen_chromeos.cc

 // Copyright (c) 2013 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.
 
 #include "chrome/browser/fullscreen.h"
 
 #include "ash/root_window_controller.h"
 
 bool IsFullScreenMode() {
   ash::internal::RootWindowController* controller =
       ash::internal::RootWindowController::ForActiveRootWindow();
-  return controller && controller->GetFullscreenWindow();
+  return controller && controller->GetTopmostFullscreenWindow();
 }