Roll engine 839b34cc687c..04274160e60c (3 commits) (#49011)

https://github.com/flutter/engine/compare/839b34cc687c...04274160e60c

git log 839b34cc687c..04274160e60c --first-parent --oneline
2020-01-16 dworsham@google.com Fix Opacity performance regression on Fuchsia (flutter/engine#15573)
2020-01-16 nurhan@google.com [web] edge launcher for windows (flutter/engine#15690)
2020-01-16 jason-simmons@users.noreply.github.com [web] Add BoxHeightStyle.strut (flutter/engine#15694)


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

-839b34cc687cd7ae2cdee2d145b36f4ce317c450
+04274160e60cafc4b5c843d7968fce241d50f03d