Eliminate ash::internal namespace

ash/wm/panels/panel_layout_manager.h

Index: ash/wm/panels/panel_layout_manager.h
diff --git a/ash/wm/panels/panel_layout_manager.h b/ash/wm/panels/panel_layout_manager.h
index 2d17b2d37f3d9154c4e3aead54a7659de4511547..f0c093d48c2bb83377090c890b4f44060da7bf0f 100644
--- a/ash/wm/panels/panel_layout_manager.h
+++ b/ash/wm/panels/panel_layout_manager.h
@@ -36,10 +36,8 @@ class Widget;
 }
 
 namespace ash {
-class Shelf;
-
-namespace internal {
 class PanelCalloutWidget;
+class Shelf;
 class ShelfLayoutManager;
 
 // PanelLayoutManager is responsible for organizing panels within the
@@ -186,7 +184,6 @@ class ASH_EXPORT PanelLayoutManager
   DISALLOW_COPY_AND_ASSIGN(PanelLayoutManager);
 };
 
-}  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_WM_PANELS_PANEL_LAYOUT_MANAGER_H_