3a17b67353
Towards https://github.com/flutter/flutter/issues/51421. Asserts some state we would not like to be hit by in integration tests using `Flutter*TestDriver`. In addition, adds a tag that can be used to run all tests that currently use this pattern: ```sh flutter test --tags flutter-test-driver ``` This showcases processes leaking quite a bit: <https://gist.github.com/matanlurey/190d9084d3a45bc5737b8406bc05b4cd>.