Roll external/skia 3cc809294..4f8c8f839 (3 commits)

https://skia.googlesource.com/skia.git/+log/3cc809294..4f8c8f839

2017-11-29 robertphillips@google.com Revert "Make PathGeoBuilder use consistent iterators."
2017-11-29 bsalomon@google.com Revert "Make PathGeoBuilder use consistent iterators."
2017-11-29 bsalomon@google.com Make PathGeoBuilder use consistent iterators.

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: Idff2437c04156ae1aed40cf4c10db5b13a8e3f1d
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.