Currently, "root_build_dir" doesn't work in args.gn file, and GN complains that '"root_build_dir" is not currently in scope.'. For example: input_file="$root_build_dir/some_file.txt".

We want this because it will make it much easier to pass a file that is within root build directory to args.gn file.

brettw@, dpranke@, do you have any concerns with implementing this?