Goroutine leak checking is still too tedious, so untested.

See #6705 which is my fault for forgetting to mail out.

Change-Id: I899fb311c9d4229ff1dbd3f54fe307805e17efee
Reviewed-on: https://go-review.googlesource.com/22581Reviewed-by: Ahmed W. <oneofone@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>