Move SetUseOverrideRedirectWindowByDefault() to //ui/base.

ui/base/platform_window_defaults.h

+// Copyright 2017 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_BASE_PLATFORM_WINDOW_DEFAULTS_H_
+#define UI_BASE_PLATFORM_WINDOW_DEFAULTS_H_
+
+#include "ui/base/ui_base_export.h"
+
+namespace ui {
+
+// Returns true if PlatformWindow should use test configuration. Will return
+// false by default, unless test::EnableTestConfigForPlatformWindows() has been
+// called, then it will return true.
+UI_BASE_EXPORT bool UseTestConfigForPlatformWindows();
+
+namespace test {
+
+// Sets that PlatformWindow should use test configuration. This can safely be
+// called on all platforms but only has an effect for X11.
+
+// For X11 this sets the value of the |override_redirect| attribute used when
+// creating an X11 window to true. It is necessary to set this flag on for
+// various tests, otherwise the call to Show() blocks because it never receives
+// the MapNotify event. It is unclear why this is necessary, but might be
+// related to calls to XInitThreads().
+UI_BASE_EXPORT void EnableTestConfigForPlatformWindows();
+
+}  // namespace test
+}  // namespace ui
+
+#endif  // UI_BASE_PLATFORM_WINDOW_DEFAULTS_H_