Roll external/skia 8716b50aa..e2d4e8f27 (3 commits)

https://skia.googlesource.com/skia.git/+log/8716b50aa..e2d4e8f27

2018-01-02 liyuqian@google.com Stronger fix for swapping r0, r1 in 2pt conical gradients
2018-01-02 fmalita@chromium.org [skotty,sksg] Initial RRect support
2018-01-02 reed@google.com share impl between makeNonTexture and makeRaster

The AutoRoll server is located here: https://android-roll.skia.org

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
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Test: Presubmit checks will test this change.
Change-Id: I4f96dc50e32f8ca52b029f8a708651b30cc64ec2
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