Creates AXPosition to uniquely identify a position in the accessibility tree

ui/accessibility/ax_range.h

Index: ui/accessibility/ax_range.h
diff --git a/ui/accessibility/ax_range.h b/ui/accessibility/ax_range.h
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+++ b/ui/accessibility/ax_range.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_RANGE_H_
+#define UI_ACCESSIBILITY_AX_RANGE_H_
+
+#include "ui/accessibility/ax_position.h"
+
+namespace ui {
+
+// A range of ax positions.
+template <AXNodeType>
+struct AXRange {
+  AXRange()
+      : anchor(AXPosition<AXNodeType>::CreateNullPosition()),
+        focus(AXPosition<AXNodeType>::CreateNullPosition()) {}
+
+  AXRange(AXPosition<AXNodeType> anchor, AXPosition<AXNodeType> focus)
+      : anchor(anchor), focus(focus) {}
+
+  virtual ~AXRange() {}
+
+  bool IsNull() const {
+    return anchor.IsNullPosition() || focus.IsNullPosition();
+  }
+
+  AXPosition<AXNodeType> anchor;
+  AXPosition<AXNodeType> focus;
+};
+
+}  // namespace ui
+
+#endif  // UI_ACCESSIBILITY_AX_RANGE_H_