Roll external/skia a94670bd0..06a7257b4 (1 commits)

https://skia.googlesource.com/skia.git/+log/a94670bd0..06a7257b4

2019-04-18 borenet@google.com [infra] Fixes for chrome_release_branch

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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: I430f1ee1cfcbe36255a144489f28f424631b3b8c
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.