Hide AXPlatformNode on ChromeOS.

ui/accessibility/platform/ax_platform_unique_id.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_ACCESSIBILITY_PLATFORM_AX_PLATFORM_UNIQUE_ID_H_
+#define UI_ACCESSIBILITY_PLATFORM_AX_PLATFORM_UNIQUE_ID_H_
+
+#include <stdint.h>
+
+#include "ui/accessibility/ax_export.h"
+
+namespace ui {
+
+// Each platform accessibility object has a unique id that's guaranteed to be a
+// positive number. (It's stored in an int32_t as opposed to uint32_t because
+// some platforms want to negate it, so we want to ensure the range is below the
+// signed int max.) This can be used when the id has to be unique across
+// multiple frames, since node ids are only unique within one tree.
+int32_t AX_EXPORT GetNextAXPlatformNodeUniqueId();
+
+}  // namespace ui
+
+#endif  // UI_ACCESSIBILITY_PLATFORM_AX_PLATFORM_UNIQUE_ID_H_