Roll external/skia 72859cbb1..5c7279677 (3 commits)

https://skia.googlesource.com/skia.git/+log/72859cbb1..5c7279677

2017-08-22 bsalomon@google.com Deinline methods of SkClipStack::Element
2017-08-22 angle-deps-roller@chromium.org Roll skia/third_party/externals/angle2/ d8105a03f..61bd99946 (1 commit)
2017-08-22 brianosman@google.com Add "none" option for --pr, to force software path renderer

Test: Presubmit checks will test this change.
Change-Id: I16bef7bbf388d8f9731772f3b03de1c22485e5f5