Roll external/skia 5141d215e..db816992b (4 commits)

https://skia.googlesource.com/skia.git/+log/5141d215e..db816992b

2017-08-23 benjaminwagner@google.com Update Mac CPU tasks to 10.12.
2017-08-23 senorblanco@chromium.org Fix artifacts on tiny stroked paths scaled up a lot.
2017-08-23 robertphillips@google.com Revert "GrTessellator: when sanitizing contours, remove non-finite points."
2017-08-23 reed@google.com remove code associated with legacy affine imageshaders

Test: Presubmit checks will test this change.
Change-Id: Ib93b2b19935c196230f5655faa1e1795ef197160