Converts overview to use common ash types

ash/wm/common/wm_shell_window_ids.h

Index: ash/wm/common/wm_shell_window_ids.h
diff --git a/ash/wm/common/wm_shell_window_ids.h b/ash/wm/common/wm_shell_window_ids.h
index 4c6ed096c89922c518eb3162145f94f4c71ad772..b9aa45e3e795b22f2948fecbb8fc70e1e824fa81 100644
--- a/ash/wm/common/wm_shell_window_ids.h
+++ b/ash/wm/common/wm_shell_window_ids.h
@@ -52,6 +52,10 @@ const int kShellWindowId_MenuContainer = 19;
 // The container for drag/drop images and tooltips.
 const int kShellWindowId_DragImageAndTooltipContainer = 20;
 
+// The container for special components overlaid onscreen, such as the
+// region selector for partial screenshots.
+const int kShellWindowId_OverlayContainer = 22;
+
 // ID of the window created by PhantomWindowController or DragWindowController.
 const int kShellWindowId_PhantomWindow = 23;