Use text affinity to return correct accessible line boundaries.

ui/accessibility/ax_tree_data.h

 // Copyright 2015 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_TREE_DATA_H_
 #define UI_ACCESSIBILITY_AX_TREE_DATA_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 38 matching lines @@
   std::string mimetype;
   std::string title;
   std::string url;
 
   // The node with keyboard focus within this tree, if any, or -1 if no node
   // in this tree has focus.
   int32_t focus_id;
 
   // The current text selection within this tree, if any, expressed as the
   // node ID and character offset of the anchor (selection start) and focus
-  // (selection end).
+  // (selection end). If the offset could correspond to a position on two
+  // different lines, sel_upstream_affinity means the cursor is on the first
+  // line, otherwise it's on the second line.
   int32_t sel_anchor_object_id;
   int32_t sel_anchor_offset;
+  ui::AXTextAffinity sel_anchor_affinity;
   int32_t sel_focus_object_id;
   int32_t sel_focus_offset;
+  ui::AXTextAffinity sel_focus_affinity;
 };
 
 AX_EXPORT bool operator==(const AXTreeData& lhs, const AXTreeData& rhs);
 AX_EXPORT bool operator!=(const AXTreeData& lhs, const AXTreeData& rhs);
 
 }  // namespace ui
 
 #endif  // UI_ACCESSIBILITY_AX_TREE_DATA_H_