You can view the widget rebuilt counts for the current screen and
frame in the Flutter plugin for Android Studio and IntelliJ.
For details on how to do this, see Show performance data

Benchmarking

You can measure and track your app’s performance by writing
benchmark tests. The Flutter Driver library provides support
for benchmarking. Using this integration test framework,
you can generate metrics to track the following:

Jank

Download size

Battery efficiency

Startup time

Tracking these benchmarks allows you to be informed when a
regression is introduced that adversely affects performance.

For more information, see Integration testing,
a section in Testing Flutter apps.

Other resources

The following resources provide more information on using
Flutter’s tools and debugging in Flutter:

Debugging

Flutter inspector