Creates AXPosition to uniquely identify a position in the accessibility tree

ui/accessibility/ax_node_position.cc

Index: ui/accessibility/ax_node_position.cc
diff --git a/ui/accessibility/ax_node_position.cc b/ui/accessibility/ax_node_position.cc
new file mode 100644
index 0000000000000000000000000000000000000000..28005465e1b255619c8764bd5e75a0db881c1d54
--- /dev/null
+++ b/ui/accessibility/ax_node_position.cc
@@ -0,0 +1,63 @@
+// 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.
+
+#include "ui/accessibility/ax_node_position.h"
+
+#include "base/strings/string16.h"
+#include "ui/accessibility/ax_enums.h"
+
+namespace ui {
+
+AXTree* AXNodePosition::tree_ = nullptr;
+
+AXNodePosition::AXNodePosition() {}
+
+AXNodePosition::~AXNodePosition() {}
+
+int32_t AXNodePosition::AnchorChildID(int child_index) const {
+  if (child_index < 0 || child_index >= AnchorChildCount())
+    return AXPosition::INVALID_ANCHOR_ID;
+
+  AXNode* child = GetAnchor()->ChildAtIndex(child_index);
+  DCHECK(child);
+  int32_t child_id = child->id();
+  DCHECK_NE(child_id, AXPosition::INVALID_ANCHOR_ID);
+  return child_id;
+}
+
+int AXNodePosition::AnchorChildCount() const {
+  return GetAnchor() ? GetAnchor()->child_count() : 0;
+}
+
+int AXNodePosition::AnchorIndexInParent() const {
+  return GetAnchor() ? GetAnchor()->index_in_parent()
+                     : AXPosition::INVALID_INDEX;
+}
+
+int32_t AXNodePosition::AnchorParentID() const {
+  if (!GetAnchor() || !GetAnchor()->parent())
+    return INVALID_ANCHOR_ID;
+  return GetAnchor()->parent()->id();
+}
+
+AXNode* AXNodePosition::GetNodeInTree(int tree_id, int32_t node_id) const {
+  if (!tree_ || node_id == AXPosition::INVALID_ANCHOR_ID)
+    return nullptr;
+  return AXNodePosition::tree_->GetFromId(node_id);
+}
+
+int AXNodePosition::MaxTextOffset() const {
+  if (IsTextPosition()) {
+    DCHECK(GetAnchor());
+    base::string16 name =
+        GetAnchor()->data().GetString16Attribute(AX_ATTR_NAME);
+    return static_cast<int>(name.length());
+  } else if (IsTreePosition()) {
+    return 0;
+  }
+
+  return AXPosition::INVALID_INDEX;
+}
+
+}  // namespace ui