Roll Skia from b4e5a9192d39 to b6689e568050 (2 revisions)

https://skia.googlesource.com/skia.git/+log/b4e5a9192d39..b6689e568050

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://skia-autoroll.corp.goog/r/android-master-autoroll
Please CC nifong@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

Test: Presubmit checks will test this change.
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.
Change-Id: I39db9e4b29b33b80126c2f6bfff3b190a378cc00