Roll engine 04274160e60c..85a8ac4255a8 (2 commits) (#49012)

https://github.com/flutter/engine/compare/04274160e60c...85a8ac4255a8

git log 04274160e60c..85a8ac4255a8 --first-parent --oneline
2020-01-17 dnfield@google.com Make internal cache vars private (flutter/engine#15699)
2020-01-16 skia-flutter-autoroll@skia.org Roll src/third_party/dart e33b9e2d265a..f1df196ddfe4 (24 commits) (flutter/engine#15702)


If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC jimgraham@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

bin/internal/engine.version

-04274160e60cafc4b5c843d7968fce241d50f03d
+85a8ac4255a8a7b79976ddec66a743abedc4709f