Roll external/skia 8e8fec729..f4f6bbfad (4 commits)

https://skia.googlesource.com/skia.git/+log/8e8fec729..f4f6bbfad

2018-07-27 herb@google.com Duplicate drawDFPosText into drawDFGlyphRun
2018-07-27 ethannicholas@google.com Fixed GLSL header line ordering
2018-07-27 ziadb@google.com SkAR Java: DrawManager dox and minor changes, removed unnecessary files
2018-07-27 robertphillips@google.com Fix TSAN bug in TransferPixelsTest

The AutoRoll server is located here: https://android-master-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.
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.

Bug: 111582212
Change-Id: I7851ec45dd32f58ae5642a850355b07b0d5f9dd8