TestName: Make 'name' field volatile

[rschmitt]

This ensures that the name is published across threads correctly--for
instance, if a parallelized runner is used.

[kcooney]

Merged. Thanks!

I think in practice, we were probably fine, since it would be hard for a thread that did not update that field to get a reference to the rule. But making it volatile is safer and there's almost no overhead on most processors.

[rschmitt]

Suppose you have a Timeout downstream of TestName. The name field will be set, and then Timeout will spawn a separate thread in which the actual test will run. Currently this should be safe because it creates a new Thread object for every test invocation, but if this implementation detail ever changed (e.g. Timeout reuses threads in a thread pool) undefined behavior will result.

[kcooney]

Ah, I see. I could easily imagine custom Timeout implementations that use a thread pool