Roll external/skia ae79f32e7..671abd176 (1 commits)

https://skia.googlesource.com/skia.git/+log/ae79f32e7..671abd176

2017-08-20 update-skps@skia.org Update SKP version

Test: Presubmit checks will test this change.
Change-Id: I5ae1b643695c732ea31a2afe44956129cfa65f7d