Use relative bounding boxes throughout Chrome accessibility

ui/accessibility/ax_node_data.h

 // Copyright 2013 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_DATA_H_
 #define UI_ACCESSIBILITY_AX_NODE_DATA_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 95 matching lines @@
   uint32_t state;
   std::vector<std::pair<AXStringAttribute, std::string>> string_attributes;
   std::vector<std::pair<AXIntAttribute, int32_t>> int_attributes;
   std::vector<std::pair<AXFloatAttribute, float>> float_attributes;
   std::vector<std::pair<AXBoolAttribute, bool>> bool_attributes;
   std::vector<std::pair<AXIntListAttribute, std::vector<int32_t>>>
       intlist_attributes;
   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.
   // NOTE: this member is a std::unique_ptr because it's rare and gfx::Transform
   // takes up a fair amount of space. The assignment operator and copy
   // constructor both make a duplicate of the owned pointer, so it acts more
   // like a member than a pointer.
   std::unique_ptr<gfx::Transform> transform;
 };
 
 }  // namespace ui
 
 #endif  // UI_ACCESSIBILITY_AX_NODE_DATA_H_