Refactors DockedWindowLayoutManager in terms of ash/wm/common

ash/system/web_notification/web_notification_tray.cc

Index: ash/system/web_notification/web_notification_tray.cc
diff --git a/ash/system/web_notification/web_notification_tray.cc b/ash/system/web_notification/web_notification_tray.cc
index 1f2e461c95c567976f03fc0f74621244719ffb6d..a7fc6c844e25e9010ecb70eeb2c41bf878d91511 100644
--- a/ash/system/web_notification/web_notification_tray.cc
+++ b/ash/system/web_notification/web_notification_tray.cc
@@ -303,7 +303,7 @@ void WebNotificationTray::UpdateAfterLoginStatusChange(
   OnMessageCenterTrayChanged();
 }
 
-void WebNotificationTray::SetShelfAlignment(ShelfAlignment alignment) {
+void WebNotificationTray::SetShelfAlignment(wm::ShelfAlignment alignment) {
   if (alignment == shelf_alignment())
     return;
   TrayBackgroundView::SetShelfAlignment(alignment);