- Fix flutter_aot_app template for moved Flutter tool GN label.
- Add missing dart:io tree-shaking roots.
- Add example AOT app to catch future breakage.
... and reattach fitness to the build. We detached fitness from the build
because it was seeing an old version of playfair that didn't work with the most
recent version of the Sky package.
Unhook fitness from the build to work around build break in playfair. We
updated the Sky package in an incompatible way, which means we need to roll in
a new playfair package to build fitness.
