Refactors DockedWindowLayoutManager in terms of ash/wm/common

ash/system/status_area_widget_delegate.cc

Index: ash/system/status_area_widget_delegate.cc
diff --git a/ash/system/status_area_widget_delegate.cc b/ash/system/status_area_widget_delegate.cc
index bce3ef583e30e2880329c6e06890e5fd6a8f272c..c87869a631a5689293090339d77641f38bd82f35 100644
--- a/ash/system/status_area_widget_delegate.cc
+++ b/ash/system/status_area_widget_delegate.cc
@@ -49,8 +49,8 @@ class StatusAreaWidgetDelegateAnimationSettings
 namespace ash {
 
 StatusAreaWidgetDelegate::StatusAreaWidgetDelegate()
-    : focus_cycler_for_testing_(NULL),
-      alignment_(SHELF_ALIGNMENT_BOTTOM) {
+    : focus_cycler_for_testing_(nullptr),
+      alignment_(wm::SHELF_ALIGNMENT_BOTTOM) {
   // Allow the launcher to surrender the focus to another window upon
   // navigation completion by the user.
   set_allow_deactivate_on_esc(true);