Refactors DockedWindowLayoutManager in terms of ash/wm/common

ash/system/status_area_widget.cc

Index: ash/system/status_area_widget.cc
diff --git a/ash/system/status_area_widget.cc b/ash/system/status_area_widget.cc
index 09bb1519ad3797421f30ee0c67c44b79afaa5c6a..611e402d781296fd1e7638764827760acd35986c 100644
--- a/ash/system/status_area_widget.cc
+++ b/ash/system/status_area_widget.cc
@@ -163,7 +163,7 @@ void StatusAreaWidget::AddOverviewButtonTray() {
   status_area_widget_delegate_->AddTray(overview_button_tray_);
 }
 
-void StatusAreaWidget::SetShelfAlignment(ShelfAlignment alignment) {
+void StatusAreaWidget::SetShelfAlignment(wm::ShelfAlignment alignment) {
   status_area_widget_delegate_->set_alignment(alignment);
   if (system_tray_)
     system_tray_->SetShelfAlignment(alignment);