Get rid of AX_LINE_BREAKS attribute to improve performance.

ui/accessibility/ax_enums.idl

Index: ui/accessibility/ax_enums.idl
diff --git a/ui/accessibility/ax_enums.idl b/ui/accessibility/ax_enums.idl
index b85951d325fb0cbfbd4cee2bdc7b8489ccbff12c..942370be99eeaf3a83ac76a4954785df46cee38a 100644
--- a/ui/accessibility/ax_enums.idl
+++ b/ui/accessibility/ax_enums.idl
@@ -390,9 +390,6 @@
     flowto_ids,
     labelledby_ids,
 
-    // For static text. Character indices where line breaks occur.
-    line_breaks,
-
     // For static text. These int lists must be the same size; they represent
     // the start and end character offset of each marker. Examples of markers
     // include spelling and grammar errors, and find-in-page matches.
@@ -416,6 +413,12 @@
     // within the object's bounds, the second offset is the right coordinate
     // of the second character, and so on.
     character_offsets,
+    
+    // Used for caching. Do not read directly. Use
+    // |AXNode::GetOrComputeLineStartOffsets|
+    // For all text fields and content editable roots: A list of the start
+    // offsets of each line inside this object.
+    cached_line_starts,
 
     // For inline text. These int lists must be the same size; they represent
     // the start and end character offset of each word within this text.