Roll external/skia 937348d4d..bdb32d179 (1 commits)

https://skia.googlesource.com/skia.git/+log/937348d4d..bdb32d179

2018-09-24 brianosman@google.com Remove SkPM4f::toF16

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: I2a60571323dda6e66102a5d6d32b71073ae09be7
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.