Add an explicit WriteString method to closeOnce that acquires the
writers lock. This overrides the one promoted from the
embedded *os.File field. The promoted one naturally does not acquire
the lock, and can therefore race with the Close method.
Fixes #17647.
Change-Id: I3460f2a0d503449481cfb2fd4628b4855ab0ecdf
Reviewed-on: https://go-review.googlesource.com/33298
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>