More precise break points and stepping when debugging...

src/parser.cc

Index: src/parser.cc
===================================================================
--- src/parser.cc	(revision 4816)
+++ src/parser.cc	(working copy)
@@ -2867,10 +2867,13 @@
   // In parsing the first assignment expression in conditional
   // expressions we always accept the 'in' keyword; see ECMA-262,
   // section 11.12, page 58.
+  int left_position = scanner().peek_location().beg_pos;
   Expression* left = ParseAssignmentExpression(true, CHECK_OK);
   Expect(Token::COLON, CHECK_OK);
+  int right_position = scanner().peek_location().beg_pos;
   Expression* right = ParseAssignmentExpression(accept_IN, CHECK_OK);
-  return NEW(Conditional(expression, left, right));
+  return NEW(Conditional(expression, left, right,
+                         left_position, right_position));
 }