Set the timeDilation variable (from the scheduler
library) to a number greater than 1.0, for instance, 50.0.
It’s best to only set this once on app startup. If you
change it on the fly, especially if you reduce it while
animations are running, it’s possible that the framework
will observe time going backwards, which will probably
result in asserts and generally interfere with your efforts.

Debug flags: performance

Note:
  You can achieve similar results to some of these debug
  flags using DevTools. Some of the debug flags aren’t
  particularly useful. If you find a flag that has
  functionality you would like to see added to DevTools,
  please file an issue.