Hook up the FocusController behind a flag.

ash/wm/workspace_controller.cc

 // 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.
 
 #include "ash/wm/workspace_controller.h"
 
 #include "ash/ash_switches.h"
 #include "ash/wm/window_util.h"
 #include "ash/wm/workspace/workspace_manager.h"
 #include "base/command_line.h"
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/window.h"
 
 namespace ash {
 namespace internal {
 
 WorkspaceController::WorkspaceController(aura::Window* viewport)
-    : viewport_(viewport) {
+    : ActivationChangeShim(viewport->GetRootWindow()),
+      viewport_(viewport) {
   aura::RootWindow* root_window = viewport->GetRootWindow();
   workspace_manager_.reset(new WorkspaceManager(viewport));
   aura::client::GetActivationClient(root_window)->AddObserver(this);
 }
 
 WorkspaceController::~WorkspaceController() {
   aura::client::GetActivationClient(viewport_->GetRootWindow())->
       RemoveObserver(this);
 }
 
@@ skipping 19 matching lines @@
 }
 
 void WorkspaceController::OnWindowActivated(aura::Window* window,
                                             aura::Window* old_active) {
   if (!window || window->GetRootWindow() == viewport_->GetRootWindow())
     workspace_manager_->SetActiveWorkspaceByWindow(window);
 }
 
 }  // namespace internal
 }  // namespace ash