Move SetUseOverrideRedirectWindowByDefault() to //ui/base.

ui/platform_window/x11/x11_window_base.h

Index: ui/platform_window/x11/x11_window_base.h
diff --git a/ui/platform_window/x11/x11_window_base.h b/ui/platform_window/x11/x11_window_base.h
index 9e7e17be1a735afad4d1634ea3e3abb9e95e8bcd..b944d296cade1224caaa2015790ada61922fcdc4 100644
--- a/ui/platform_window/x11/x11_window_base.h
+++ b/ui/platform_window/x11/x11_window_base.h
@@ -79,19 +79,6 @@ class X11_WINDOW_EXPORT X11WindowBase : public PlatformWindow {
   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_