Adds analysis error tracking and fixes the enum declaration to not produce a warning.
I'm not happy with `assertNoAnalysisErrors` and would like something more configurable and context-aware but haven't thought it fully through.
Maybe something like:
```
assertNoErrors(
except: ['unused_import'],
);
```
(And maybe a file and line number?)
Alternatively, we could add ignores to the test sources:
```
import 'a.dart'; // ignore: unused_import
```
and maybe special case the line we're completing on:
```
f(^);
```
Still mulling it all over but your thoughts are welcome!
Change-Id: I1d0c5fbd72c80dde13ae98cb76c3728ab00a12f9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/135440
Commit-Queue: Phil Quitslund <pquitslund@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
pq
5fd18be9c5