Roll external/skia 02ab8cc29..a377184a5 (1 commits)

https://skia.googlesource.com/skia.git/+log/02ab8cc29..a377184a5

2017-05-05 mtklein@chromium.org Retry "Factor out common code from sweep and linear."

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Change-Id: I5aa58e321e367fd2df7b35a71d0f529586a67584