Roll external/skia 42adc7989..3167aa0c9 (1 commits)

https://skia.googlesource.com/skia.git/+log/42adc7989..3167aa0c9

2018-01-14 update-skps@skia.org Update SKP version

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
be CC'd on the roll, and stop the roller if necessary.

Test: Presubmit checks will test this change.
Change-Id: I7118f3420c87df8270e273a9c5d9a4574c6fc3ad
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.