gn: attach comments to parse tree

tools/gn/header_checker.cc

Index: tools/gn/header_checker.cc
diff --git a/tools/gn/header_checker.cc b/tools/gn/header_checker.cc
index 78c619bbaaa333ad698e135d025f6af8cdd0bb35..26bc2222e9ec98e999a284da4c25a02f4b6d9f08 100644
--- a/tools/gn/header_checker.cc
+++ b/tools/gn/header_checker.cc
@@ -60,11 +60,14 @@ LocationRange CreatePersistentRange(const InputFile& input_file,
       input_file.name(), &clone_input_file, &tokens, &parse_root);
   clone_input_file->SetContents(input_file.contents());
 
-  return LocationRange(
-      Location(clone_input_file, range.begin().line_number(),
-               range.begin().char_offset()),
-      Location(clone_input_file, range.end().line_number(),
-               range.end().char_offset()));
+  return LocationRange(Location(clone_input_file,
+                                range.begin().line_number(),
+                                range.begin().char_offset(),
+                                -1 /* TODO(scottmg) */),
+                       Location(clone_input_file,
+                                range.end().line_number(),
+                                range.end().char_offset(),
+                                -1 /* TODO(scottmg) */));
 }
 
 // Given a reverse dependency chain where the target chain[0]'s includes are