simplify round_down_to_int by using ceil instead of floor

BUG=skia:

Change-Id: I465d98d6b0d97e1ede82670c663f9695b5a0a1de
Reviewed-on: https://skia-review.googlesource.com/7041
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>
1 file changed