Refactors DockedWindowLayoutManager in terms of ash/wm/common

ash/system/overview/overview_button_tray.cc

Index: ash/system/overview/overview_button_tray.cc
diff --git a/ash/system/overview/overview_button_tray.cc b/ash/system/overview/overview_button_tray.cc
index eb6dce8866f6b9957f09a399f5dbc0199e9b5ee3..1d68e628c369f783a5a4cd89ba6b173803e9a050 100644
--- a/ash/system/overview/overview_button_tray.cc
+++ b/ash/system/overview/overview_button_tray.cc
@@ -99,7 +99,7 @@ void OverviewButtonTray::HideBubbleWithView(
   // This class has no bubbles to hide.
 }
 
-void OverviewButtonTray::SetShelfAlignment(ShelfAlignment alignment) {
+void OverviewButtonTray::SetShelfAlignment(wm::ShelfAlignment alignment) {
   if (alignment == shelf_alignment())
     return;