Roll engine be4c8338a6ab..4b6b4afd6492 (2 commits) (#38498)

git@github.com:flutter/engine.git/compare/be4c8338a6ab...4b6b4afd6492

git log be4c8338a6ab..4b6b4afd6492 --no-merges --oneline
2019-08-13 skia-flutter-autoroll@skia.org Roll src/third_party/skia cd8b6d5c1cb8..f75996469d02 (5 commits) (flutter/engine#10984)
2019-08-13 chinmaygarde@google.com Allow embedder controlled composition of Flutter layers. (flutter/engine#10195)

The AutoRoll server is located here: https://autoroll.skia.org/r/flutter-engine-flutter-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 (stuartmorgan@google.com), and stop
the roller if necessary.

bin/internal/engine.version

-be4c8338a6ab36989ec2ade1c780d96fe1b52f31
+4b6b4afd6492499b72bdc59c3a633c7721708087