Reduce absolute paths in generated ninja files in skia

BUG=chromium:723856

Change-Id: Ifa065daddfe1d775e843307587e4007ad6dae6d4
Reviewed-on: https://skia-review.googlesource.com/17802
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
1 file changed