Run all microbenchmarks

[jtmcdole]

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.

[jtmcdole]

Mac+iOS

> time ../../bin/cache/dart-sdk/bin/dart bin/test_runner.dart test -t microbenchmarks_ios -d <my device>

  25.68s user 9.63s system 17% cpu 3:19.04 total

Mac+Android

time ../../bin/cache/dart-sdk/bin/dart bin/test_runner.dart test -t microbenchmarks -d <my other device>
  8.00s user 2.63s system 7% cpu 2:20.63 total

[zanderso]

Does this README need an update? https://github.com/flutter/flutter/blob/master/dev/benchmarks/microbenchmarks/README.md

It'll be interesting to see whether there are shifts in the metrics in the benchmarks that come later in the sequence. That would indicate that we still have some post-install or first-run warmup happening somewhere.

[jtmcdole]

Does this README need an update? https://github.com/flutter/flutter/blob/master/dev/benchmarks/microbenchmarks/README.md

It'll be interesting to see whether there are shifts in the metrics in the benchmarks that come later in the sequence. That would indicate that we still have some post-install or first-run warmup happening somewhere.

I'll update it. I ran the benchmarks against a mokey and an iphone se and they were comperable to skia perf numbers.

[jtmcdole]

Does this README need an update? https://github.com/flutter/flutter/blob/master/dev/benchmarks/microbenchmarks/README.md

It'll be interesting to see whether there are shifts in the metrics in the benchmarks that come later in the sequence. That would indicate that we still have some post-install or first-run warmup happening somewhere.

Done.