This tests static analysis on the ddc patch, but not the dart2js one yet.
It also fixes js/null_test.dart to ensure it passes. Note, that test was broken independent of NNBD.
Change-Id: I5a6bfdfaac845eaba6f154d30f2c1e30199574d0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/131300
Commit-Queue: Vijay Menon <vsm@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>