* Switch build to using generated headers

* Update DEPS to pick up newer buildroot

* Only run hook on Windows

https://dart.googlesource.com/sdk.git/+log/b191fb71063c..64a5583ffbc9

2021-03-08 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.13.0-116.0.dev
2021-03-07 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.13.0-115.0.dev

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dart-sdk-flutter-engine
Please CC dart-vm-team@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/+doc/master/autoroll/README.md

https://skia.googlesource.com/skia.git/+log/5f2932e0e391..07ee548d5bcd

2021-03-07 reed@google.com Remove legacy picture-shader impl

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/skia-flutter-autoroll
Please CC kjlubick@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/+doc/master/autoroll/README.md