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 1b9fd854a17d4eee88015747dba50dfd2588e0e2..54891c7fae5680644ae0df21a0b1b3dd9beb85e9 100644
--- a/ash/wm/workspace_controller.cc
+++ b/ash/wm/workspace_controller.cc
@@ -42,21 +42,18 @@ bool IsDockedAreaVisible(const ShelfLayoutManager* shelf) {
 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());
 }