Use text affinity to return correct accessible line boundaries.

ui/accessibility/ax_enums.idl

 // Copyright 2014 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.
 
 // These should be kept in sync with third_party/WebKit/public/web/WebAXEnums.h
 // until the Chromium and Blink trees are merged.
 [camel_case_enum_to_string=true] namespace ui {
 
   // For new entries to the following three enums, also add to
   // chrome/common/extensions/api/automation.idl.
@@ skipping 490 matching lines @@
     swipe_down_2,
     swipe_left_3,
     swipe_up_3,
     swipe_right_3,
     swipe_down_3,
     swipe_left_4,
     swipe_up_4,
     swipe_right_4,
     swipe_down_4
   };
+
+  enum AXTextAffinity {
+    downstream = 0,
+    upstream = 1
+  };
 };