Move SetUseOverrideRedirectWindowByDefault() to //ui/base.

ash/test/ash_test_helper.cc

Index: ash/test/ash_test_helper.cc
diff --git a/ash/test/ash_test_helper.cc b/ash/test/ash_test_helper.cc
index a5a177e6f5d8e390a0d85de5778f4a0f2f2ab324..383e291fe9d7cbdfbfa4fb3a77aaab7836f9facc 100644
--- a/ash/test/ash_test_helper.cc
+++ b/ash/test/ash_test_helper.cc
@@ -31,6 +31,7 @@
 #include "ui/aura/test/event_generator_delegate_aura.h"
 #include "ui/base/ime/input_method_initializer.h"
 #include "ui/base/material_design/material_design_controller.h"
+#include "ui/base/platform_window_defaults.h"
 #include "ui/base/test/material_design_controller_test_api.h"
 #include "ui/compositor/scoped_animation_duration_scale_mode.h"
 #include "ui/compositor/test/context_factories_for_test.h"
@@ -41,10 +42,6 @@
 #include "ui/wm/core/cursor_manager.h"
 #include "ui/wm/core/wm_state.h"
 
-#if defined(USE_X11)
-#include "ui/aura/window_tree_host_x11.h"
-#endif
-
 namespace ash {
 namespace test {
 
@@ -54,9 +51,7 @@ AshTestHelper::AshTestHelper(AshTestEnvironment* ash_test_environment)
       test_screenshot_delegate_(nullptr),
       dbus_thread_manager_initialized_(false),
       bluez_dbus_manager_initialized_(false) {
-#if defined(USE_X11)
-  aura::test::SetUseOverrideRedirectWindowByDefault(true);
-#endif
+  ui::test::EnableTestConfigForPlatformWindows();
   aura::test::InitializeAuraEventGeneratorDelegate();
 }