Roll external/skia cdc371af3..9ec77b557 (1 commits)

https://skia.googlesource.com/skia.git/+log/cdc371af3..9ec77b557

2018-09-18 mtklein@google.com Revert "implement SkPixmap::erase() with draws"

The AutoRoll server is located here: https://autoroll-internal.skia.org/r/android-master-autoroll

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: I7e31c65a5b2c4d23f7b6279e0747ffb56402ea90
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.