Because diagnostics computations happen in parallel, we were getting
concurrent map writes by keeping one cache.
Change-Id: Ifa5adffe14c509168c9f8c5cb012f3fcd3a32441
Reviewed-on: https://go-review.googlesource.com/c/163161
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>