Creates AXPosition to uniquely identify a position in the accessibility tree

ui/accessibility/ax_node_position.h

Index: ui/accessibility/ax_node_position.h
diff --git a/ui/accessibility/ax_node_position.h b/ui/accessibility/ax_node_position.h
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index 0000000000000000000000000000000000000000..bf40bd9de8155d477cedaa669772e64ab8ae2a1c
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+++ b/ui/accessibility/ax_node_position.h
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+// 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_ACCESSIBILITY_AX_NODE_POSITION_H_
+#define UI_ACCESSIBILITY_AX_NODE_POSITION_H_
+
+#include <stdint.h>
+
+#include "ui/accessibility/ax_export.h"
+#include "ui/accessibility/ax_node.h"
+#include "ui/accessibility/ax_position.h"
+#include "ui/accessibility/ax_tree.h"
+
+namespace ui {
+
+class AX_EXPORT AXNodePosition : public AXPosition<AXNodePosition, AXNode> {
+ public:
+  AXNodePosition();
+  ~AXNodePosition() override;
+
+  static void SetTreeForTesting(AXTree* tree) { tree_ = tree; }
+
+ protected:
+  int32_t AnchorChildID(int child_index) const override;
+  int AnchorChildCount() const override;
+  int AnchorIndexInParent() const override;
+  int32_t AnchorParentID() const override;
+  AXNode* GetNodeInTree(int tree_id, int32_t node_id) const override;
+  int MaxTextOffset() const override;
+
+ private:
+  static AXTree* tree_;
+};
+
+}  // namespace ui
+
+#endif  // UI_ACCESSIBILITY_AX_NODE_POSITION_H_