Add ScopedMacRTL class for Cocoa browser RTL testing

ui/base/cocoa/rtl_feature.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_BASE_COCOA_RTL_FEATURE_H_
+#define UI_BASE_COCOA_RTL_FEATURE_H_
+
+#include "base/feature_list.h"
+#include "ui/base/ui_base_export.h"
+
+namespace ui {
+
+UI_BASE_EXPORT extern const base::Feature kExperimentalMacRTL;
+
+// Returns whether both:
+// 1) Experimental Mac RTL support is enabled via the ExperimentalMacRTL
+//    feature;
+// 2) The browser UI is in RTL mode.
+// If ExperimentalMacRTL becomes the default, this function can be replaced with
+// uses of base::i18n::IsRTL().
+UI_BASE_EXPORT bool ShouldDoExperimentalRTLLayout();
+
+// Returns true if ShouldDoExperimentalRTLLayout() is true and the OS is
+// 10.12 or above. macOS 10.12 is the first OS where the native stoplight
+// buttons are reversed in RTL, so manually reversing them in previous
+// OSes would make Chrome stick out.
+UI_BASE_EXPORT bool ShouldFlipWindowControlsInRTL();
+
+}  // namespace ui
+
+#endif  // UI_BASE_COCOA_RTL_FEATURE_H_