Use a single ToplevelWindowEventHandler for the ash::Shell

ash/wm/workspace_controller.cc

Index: ash/wm/workspace_controller.cc
diff --git a/ash/wm/workspace_controller.cc b/ash/wm/workspace_controller.cc
index 7bf6a28be9e30926d5e08fb28ceffb0a3101f110..321e858dcf0d1cf95362f9b1ddfbbe64a9095187 100644
--- a/ash/wm/workspace_controller.cc
+++ b/ash/wm/workspace_controller.cc
@@ -45,21 +45,18 @@ bool IsDockedAndVisible(const aura::Window* window) {
 WorkspaceController::WorkspaceController(aura::Window* viewport)
     : viewport_(viewport),
       shelf_(NULL),
-      event_handler_(new WorkspaceEventHandler(viewport_)) {
+      event_handler_(new WorkspaceEventHandler),
+      layout_manager_(new WorkspaceLayoutManager(viewport)) {
   SetWindowVisibilityAnimationTransition(
       viewport_, views::corewm::ANIMATE_NONE);
 
-  // The layout-manager cannot be created in the initializer list since it
-  // depends on the window to have been initialized.
-  layout_manager_ = new WorkspaceLayoutManager(viewport_);
   viewport_->SetLayoutManager(layout_manager_);
-
-  viewport_->Show();
+  viewport_->AddPreTargetHandler(event_handler_.get());
+  viewport_->AddPostTargetHandler(event_handler_.get());
 }
 
 WorkspaceController::~WorkspaceController() {
   viewport_->SetLayoutManager(NULL);
-  viewport_->SetEventFilter(NULL);
   viewport_->RemovePreTargetHandler(event_handler_.get());
   viewport_->RemovePostTargetHandler(event_handler_.get());
 }