Use relative bounding boxes throughout Chrome accessibility

ui/accessibility/ax_node_data.h

Index: ui/accessibility/ax_node_data.h
diff --git a/ui/accessibility/ax_node_data.h b/ui/accessibility/ax_node_data.h
index 7fe95e2f529e9a8a131c2d8c77549d5aa5375d9d..3fbaaa5bd41ea264e0ed0a570d028f8ce2a0bc5d 100644
--- a/ui/accessibility/ax_node_data.h
+++ b/ui/accessibility/ax_node_data.h
@@ -113,7 +113,14 @@ struct AX_EXPORT AXNodeData {
   base::StringPairs html_attributes;
   std::vector<int32_t> child_ids;
 
-  // The object's location relative to its window or frame.
+  // TODO(dmazzoni): replace the following three members with a single
+  // instance of AXRelativeBounds.
+
+  // The id of an ancestor node in the same AXTree that this object's
+  // bounding box is relative to, or -1 if there's no offset container.
+  int offset_container_id;
+
+  // The relative bounding box of this node.
   gfx::RectF location;
 
   // An additional transform to apply to position this object and its subtree.