Roll external/skia d46ffc59a202..9e951cd782c4 (3 commits)

https://skia.googlesource.com/skia.git/+log/d46ffc59a202..9e951cd782c4

2019-10-04 kjlubick@google.com Reduce bandwidth to RPIs
2019-10-04 reed@google.com Simple iterator for textblobs
2019-10-04 rmistry@google.com Update sheriff doc with autorollers and handoff doc

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 scroggo@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/+/master/autoroll/README.md

Test: Presubmit checks will test this change.
Change-Id: I6be2df5ef563fa4c505242ad8d56f17570a8ea66
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.