Roll external/skia 836ff5e40..2e346a611 (10 commits)

https://skia.googlesource.com/skia.git/+log/836ff5e40..2e346a611

2019-04-30 recipe-mega-autoroller@chops-service-accounts.iam.gserviceaccount.com Roll recipe dependencies (nontrivial).
2019-04-30 michaelludwig@google.com Upgrade to SkVx in GrQuad rendering
2019-04-30 jvanverth@google.com Use correct packing for Metal uniform arrays.
2019-04-30 recipe-mega-autoroller@chops-service-accounts.iam.gserviceaccount.com Roll recipe dependencies (trivial).
2019-04-30 mtklein@google.com Revert "Temporarily revert runtime decoder registration."
2019-04-30 halcanary@google.com Experimental Editor: begin text selection code
2019-04-30 benjaminwagner@google.com Don't use tty in win_ssh_cmd.py
2019-04-30 reed@google.com stop calling legacy 255-biased colormatrix
2019-04-30 robertphillips@google.com Suppress skinning benches for NVIDIA_Shield
2019-04-30 recipe-mega-autoroller@chops-service-accounts.iam.gserviceaccount.com Roll recipe dependencies (trivial).

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: I69d877bf4d3e625562d37c84eed73f0463edf91f
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.