Test BoringSSL refcounting

Currently, we have a few small smoke tests to make sure that we don't decrement BoringSSL refcounts too far. However, we have no tests to ensure that we decrement refcounts far enough (in other words, that we don't leak resources by leaving unused objects allocated and constructed).

We should also test the latter. The way to do this is probably to figure out how to inspect the refcount on a BoringSSL object and use that mechanism to ensure that the refcount on these objects is 1 when we only hold a single reference. That said, perhaps there's a better way to do this.

EDIT: Let's first try to see if we can enable ASan (#15), which should address this.

Start by reviewing the existing BoringSSL refcount smoke tests, then investigate issue #15 for the proposed ASan approach. The work is done when tests verify that unused BoringSSL objects are released appropriately, either through refcount inspection or the agreed sanitizer-based mechanism.

Written by the indexing model from the issue text.