Fix rewrite_includes to work in both Python 2 and 3.

This is patterned after http://review.skia.org/439776, but uses the
`six` library for Python 2/3 cross-compatibility.

Change-Id: If64c48c35d86b83c77316bb5536be6e7bd24c967
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/439936
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
1 file changed