The previous design (which stored the graph impicitly in the nodes
themselves) had a memory leak because some nullability nodes are
static, meaning that once a node became connected to one of the static
nodes, it would never be garbage collected.
Change-Id: I9821660198e29ff974ee0afa678851e0418e0527
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/101487
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
Paul Berry
078338bb1d