When running with `--no-sound-null-safety` turned on, it turns out null
is unboxed as an Mint in some cases without checking for null first.
Before, tests would fail because unboxing it would give a really
large int that was unlikely to be acceptable to subsequent range
checks and the like.
However, since 2f63ace, that memory is now zero-initialized, and zero is
more likely to be an acceptable value, so tests either fail for
unexpected reasons or, worse, unexpectedly succeed.
As a stopgap until the appropriate checks are emitted, we initialize
the contents of null with its address as an ObjectPtr like we used to.
TEST=corelib{,_2}/list_removeat_test on dartkp-* configurations.
Issue: https://github.com/dart-lang/sdk/issues/52910
Change-Id: If456d503c86202616f4f566a402118e9c41194ba
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/313500
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>
3fcf660ed1