Rename the aura_shell namespace to ash

ash/wm/root_window_event_filter.h

Index: ash/wm/root_window_event_filter.h
===================================================================
--- ash/wm/root_window_event_filter.h	(revision 115744)
+++ ash/wm/root_window_event_filter.h	(working copy)
@@ -12,7 +12,7 @@
 #include "ui/aura/event_filter.h"
 #include "ash/ash_export.h"
 
-namespace aura_shell {
+namespace ash {
 namespace internal {
 
 // RootWindowEventFilter gets all root window events first and can provide
@@ -64,6 +64,6 @@
 };
 
 }  // namespace internal
-}  // namespace aura_shell
+}  // namespace ash
 
 #endif  // ASH_WM_ROOT_WINDOW_EVENT_FILTER_H_