6fa1fcda8 Register plugins at the right time, once (flutter/engine#15979) (#49485)

https://github.com/flutter/engine/compare/f30ff4fcbf19...6fa1fcda8f78

git log f30ff4fcbf19..6fa1fcda8f78 --first-parent --oneline
2020-01-25 mklim@google.com Register plugins at the right time, once (flutter/engine#15979)


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 aaclarke@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

-f30ff4fcbf1984859066393ce2f755297b71d3d5
+6fa1fcda8f787b8740e53f16e77e9f97db4c4d1a