Roll external/skia 4e0255508749..b4f854080375 (3 commits)

https://skia.googlesource.com/skia.git/+log/4e0255508749..b4f854080375

2019-11-21 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/angle2 99bd10b70422..b8e748be6b94 (17 commits)
2019-11-21 skia-autoroll@skia-public.iam.gserviceaccount.com Roll ../src 0db96f99f73d..137e8082047a (617 commits)
2019-11-21 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/swiftshader 7e11f46ddf8e..f2c9ce1e08ed (9 commits)

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 djsollen@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: Iff63bbffd48f6c4634553d6d9aff5298f1df1664
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.