Roll external/skia de54d7c5e..abf8e41cc (8 commits)

https://skia.googlesource.com/skia.git/+log/de54d7c5e..abf8e41cc

2018-09-24 halcanary@google.com SkPDF: simplify SkPDFDevice::drawPaint.
2018-09-24 jvanverth@google.com Make sure ReflexHash grid count is reasonable
2018-09-24 michaelludwig@google.com Implement an explicit binary search-based analytic gradient colorizer
2018-09-24 mtklein@google.com use __builtin_debugtrap() in sk_abort_no_print() where possible
2018-09-24 mtklein@google.com make only valid SkRRects in FuzzPath
2018-09-24 kjlubick@google.com Remove coverage bots
2018-09-24 mtklein@google.com Reland "focus exported color apis"
2018-09-24 halcanary@google.com SkPDF: cleanup GraphicStackState

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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: Ib075745ec56fb6075b8a485fd9d702ec165246ce
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