"flutter create" adds option `--with-driver-test` that adds
dependencies to `flutter_driver` in `pubspec.yaml` and creates
a basic driver test runnable via `flutter drive
--target=test_driver/e2e.dart`
"flutter drive" new options:
- `--keep-app-running` tells the driver to not stop the app after tests
are done
- `--use-existing-app` tells the driver to not start a new app but use
an already running instance
Runs a test app and a driver test simultaneously, then stops the app.
Usage:
```
flutter drive --target=/path/to/test/app.dart
```
This command will look for `/path/to/test/app_test.dart` by
convention. We will expand into other ways of discovering tests in the
future.
1) Moved basic utility code into base/ directory to make it clear which code
doesn't depend on Flutter-specific knowldge.
2) Move the CommandRunner subclasses into a runner/ directory because these
aren't commands themselves.
