Move the concept of Activation to the Shell.

ui/aura/client/activation_client.cc

+// 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.
+
+#include "ui/aura/client/activation_client.h"
+
+#include "ui/aura/client/aura_constants.h"
+#include "ui/aura/root_window.h"
+
+namespace aura {
+
+// static
+void ActivationClient::SetActivationClient(ActivationClient* client) {
+  RootWindow::GetInstance()->SetProperty(kRootWindowActivationClient, client);
+}
+
+// static
+ActivationClient* ActivationClient::GetActivationClient() {
+  return reinterpret_cast<ActivationClient*>(
+      RootWindow::GetInstance()->GetProperty(kRootWindowActivationClient));
+}
+
+}  // namespace aura