Creates AXPosition to uniquely identify a position in the accessibility tree

content/browser/accessibility/ax_platform_position.h

Index: content/browser/accessibility/ax_platform_position.h
diff --git a/content/browser/accessibility/ax_platform_position.h b/content/browser/accessibility/ax_platform_position.h
new file mode 100644
index 0000000000000000000000000000000000000000..bfe95bfe8b84462a5adbb35287e4e721561495b1
--- /dev/null
+++ b/content/browser/accessibility/ax_platform_position.h
@@ -0,0 +1,45 @@
+// 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 CONTENT_BROWSER_ACCESSIBILITY_AX_PLATFORM_POSITION_H_
+#define CONTENT_BROWSER_ACCESSIBILITY_AX_PLATFORM_POSITION_H_
+
+#include <stdint.h>
+
+#include "content/browser/accessibility/ax_tree_id_registry.h"
+#include "content/browser/accessibility/browser_accessibility.h"
+#include "ui/accessibility/ax_position.h"
+
+namespace content {
+
+using AXTreeID = content::AXTreeIDRegistry::AXTreeID;
+
+class AXPlatformPosition : public ui::AXPosition<BrowserAccessibility> {
+ public:
+  ~AXPlatformPosition() override;
+
+ protected:
+  AXPlatformPosition(AXTreeID tree_id,
+                     int32_t anchor_id,
+                     int child_index,
+                     int text_offset,

[David Tseng, 2016/10/07 21:02:41]

Can you think of a way to combine text_offset and child_index? One can be
derived from the other.

+                     ui::AXPositionType type);
+
+  int AnchorChildCount() const override {

[David Tseng, 2016/10/07 21:02:41]

AXPosition<BrowserAccessibility> overrides

+    return GetAnchor() ? static_cast<int>(GetAnchor()->PlatformChildCount())

[David Tseng, 2016/10/07 21:02:41]

This isn't a simple getter; put in .cc

+                       : -1;

[David Tseng, 2016/10/07 21:02:41]

Name this special constant

+  }
+  AXPosition* GetChildPositionAt(int child_index) const override;
+  AXPosition* GetParentPosition() const override;
+  int AnchorIndexInParent() const override {
+    return GetAnchor() ? static_cast<int>(GetAnchor()->GetIndexInParent()) : -1;
+  }
+  BrowserAccessibility* GetNodeInTree(AXTreeID tree_id,
+                                      int32_t node_id) const override;
+  int MaxTextOffset() const override;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_ACCESSIBILITY_AX_PLATFORM_POSITION_H_