Move the concept of Activation to the Shell.

ui/aura/client/activation_client.h

+// Copyright (c) 2011 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_CLIENT_ACTIVATION_CLIENT_H_
+#define UI_AURA_CLIENT_ACTIVATION_CLIENT_H_
+#pragma once
+
+#include "ui/aura/aura_export.h"
+
+namespace aura {
+
+class Window;
+
+// An interface implemented by an object that manages window activation.
+class AURA_EXPORT ActivationClient {
+ public:
+  virtual ~ActivationClient() {}
+
+  // Activates |window|. If |window| is NULL, nothing happens.
+  virtual void ActivateWindow(Window* window) = 0;
+
+  // Deactivates |window|. What (if anything) is activated next is up to the
+  // client. If |window| is NULL, nothing happens.
+  virtual void DeactivateWindow(Window* window) = 0;
+
+  // Retrieves the active window, or NULL if there is none.
+  virtual aura::Window* GetActiveWindow() = 0;
+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_CLIENT_ACTIVATION_CLIENT_H_