Second try for

ui/aura/test/test_activation_client.h

 // Copyright (c) 2012 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.
 
 #ifndef UI_AURA_TEST_TEST_ACTIVATION_CLIENT_H_
 #define UI_AURA_TEST_TEST_ACTIVATION_CLIENT_H_
 #pragma once
 
 #include "base/compiler_specific.h"
 #include "base/logging.h"
@@ skipping 13 matching lines @@
   // Overridden from client::ActivationClient:
   virtual void ActivateWindow(Window* window) OVERRIDE;
   virtual void DeactivateWindow(Window* window) OVERRIDE;
   virtual Window* GetActiveWindow() OVERRIDE;
   virtual bool CanFocusWindow(Window* window) const OVERRIDE;
 
   // Overridden from WindowObserver:
   virtual void OnWindowDestroyed(Window* window) OVERRIDE;
 
  private:
+  void RemoveActiveWindow(Window* window);
+
   // This class explicitly does NOT store the active window in a window property
   // to make sure that storing the active window in a property is not treated as
   // part of the aura API. Assumptions to that end will cause tests that use
   // this client to fail.
-  Window* active_window_;
+  std::vector<Window*> active_windows_;
 
   DISALLOW_COPY_AND_ASSIGN(TestActivationClient);
 };
 
 }  // namespace test
 }  // namespace aura
 
 #endif  // UI_AURA_TEST_TEST_ACTIVATION_CLIENT_H_