Roll external/skia 9c98576bc..b609e6dc6 (7 commits)

https://skia.googlesource.com/skia.git/+log/9c98576bc..b609e6dc6

2018-07-17 ruiqimao@google.com added byte and ubyte types to SKSL
2018-07-17 bsalomon@google.com Remove crash when shader linking fails.
2018-07-17 brianosman@google.com Remove SkTransferFunctionBehavior
2018-07-17 bsalomon@google.com Reland "Remove interpolants are inaccurate workaround for Adreno 3xx."
2018-07-17 caryclark@skia.org polish picture and rrect docs
2018-07-17 robertphillips@google.com Revert "Reduce arbitrary opList splitting when sorting"
2018-07-17 robertphillips@google.com Reduce arbitrary opList splitting when sorting

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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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Change-Id: I81b9a7ff9f3d7359f27abf0102d0d5a91c291a15
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