Some runs of DeviceLab performance tests are run without a gitBranch option, but
still must save their results to a local file.

(Attempt to reland #85993)

This reverts commit 2175e64e.

This reverts commit 9d3563a8.

This reverts commit d4afa289.

Migrate core devicelab framework to null safety.

* [web] move e2e tests from flutter/engine to flutter/flutter
* flutter update-packages --force-upgrade

This reverts commit a1020512.

This reverts commit 2be0d57f.

This reverts commit 9846fa51.

This reverts commit 05d55157.

This reverts commit ef2879a4.