Two things:
**Re-land**: Uninstall microbenchmarks before running them.
Flakes in #153828 stem from adb saying the app isn't installed, but then failing to install wtih `-r`. Several other tests uninstall the app before trying to run it. Previous fix called uninstall between tests, but iOS takes 12 to 13 seconds to perform uninstall / install, which timed out the test. Just uninstall the one time since we only care about any lingering apps with different keys.
Potential solution #153828
**Make things go fast**
Instead of installing 21 different compilations of the same app to get results; compile and run them together. Locally on Mac+iOS, this should takes ~3 minutes instead of ~15 minutes.
* Add a microbenchmark that measures performance of flutter compute.
This benchmark should show performance improvements when compute is switched to Isolate.exit
* Fix analyzer warnings, increase warmup iterations
* Fix license header
