Move SetUseOverrideRedirectWindowByDefault() to //ui/base.

ui/platform_window/x11/x11_window_base.h

 // Copyright 2016 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_PLATFORM_WINDOW_X11_X11_WINDOW_BASE_H_
 #define UI_PLATFORM_WINDOW_X11_X11_WINDOW_BASE_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 61 matching lines @@
   base::string16 window_title_;
 
   // The bounds of |xwindow_|.
   gfx::Rect bounds_;
 
   bool window_mapped_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(X11WindowBase);
 };
 
-namespace test {
-
-// Sets the value of the |override_redirect| flag when creating an X11 window.
-// It is necessary to set this flag on for various tests, otherwise the call to
-// X11WindowBase::Show() blocks because it never receives the MapNotify event.
-// It is
-// unclear why this is necessary, but might be related to calls to
-// XInitThreads().
-X11_WINDOW_EXPORT void SetUseOverrideRedirectWindowByDefault(
-    bool override_redirect);
-
-}  // namespace test
-
 }  // namespace ui
 
 #endif  // UI_PLATFORM_WINDOW_X11_X11_WINDOW_BASE_H_