There has been a race condition that occasionally appears in test runs
on TryBots. Multiple threads perform type-checking, so they may race on
setting the fields of the *goFiles. Add a mutex to synchronize this.
Change-Id: If52c9d792c6504fc89044964998b06de7dfbd19c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/183978
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>