Keep track of fixed positioning in accessibility tree.

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 8d64ef51f39f54003f408e5c0dd17474d1cd1a7f..e418d09e49a474575386f3fde602ce8ec1bde1c1 100644
--- a/ui/accessibility/ax_node_data.h
+++ b/ui/accessibility/ax_node_data.h
@@ -132,7 +132,7 @@ struct AX_EXPORT AXNodeData {
   base::StringPairs html_attributes;
   std::vector<int32_t> child_ids;
 
-  // TODO(dmazzoni): replace the following three members with a single
+  // TODO(dmazzoni): replace the following four members with a single
   // instance of AXRelativeBounds.
 
   // The id of an ancestor node in the same AXTree that this object's
@@ -142,6 +142,9 @@ struct AX_EXPORT AXNodeData {
   // The relative bounding box of this node.
   gfx::RectF location;
 
+  // If true, the container's scroll position should be ignored.
+  bool is_fixed_positioned;
+
   // 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