Roll external/skia 8d6b2b6f6..f065907cc (4 commits)

https://skia.googlesource.com/skia.git/+log/8d6b2b6f6..f065907cc

2018-09-27 michaelludwig@google.com Reland "Implement an explicit binary search-based analytic gradient colorizer"
2018-09-27 mtklein@google.com bump NDK packages to r18
2018-09-27 mtklein@google.com add test that setLastPt() invalidates path bounds
2018-09-27 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/angle2 115e8a2625f5..122919bddd98 (1 commits)

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Change-Id: I657bc2f7054e15374621f91fd636877d52ad3b8d
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