Move SetUseOverrideRedirectWindowByDefault() to //ui/base.

ui/aura/window_tree_host_x11.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_AURA_WINDOW_TREE_HOST_X11_H_
 #define UI_AURA_WINDOW_TREE_HOST_X11_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 85 matching lines @@
   bool window_mapped_;
 
   // The bounds of |xwindow_|.
   gfx::Rect bounds_;
 
   ui::X11AtomCache atom_cache_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHostX11);
 };
 
-namespace test {
-
-// Set the default value of the override redirect flag used to
-// create a X window for WindowTreeHostX11.
-AURA_EXPORT void SetUseOverrideRedirectWindowByDefault(bool override_redirect);
-
-}  // namespace test
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_TREE_HOST_X11_H_