runtime/race: RaceChanWrongClose failure

[bradfitz]

At least freebsd-amd64-race has been seen flaking with:

https://build.golang.org/log/ab8f5e6bc23d2b18e162f2106de76fbbf5ad1a62

NoRaceChanPtr                            .
RaceChanWrongSend                        .
RaceChanWrongClose                       FAILED
RaceChanSendClose                        .
RaceChanSendSelectClose                  .
RaceSelectReadWriteAsync                 .
...
Passed 341 of 342 tests (99.71%, 0+, 1-)
0 expected failures (0 has not fail)
--- FAIL: TestRace (7.56s)
FAIL
FAIL    runtime/race    9.200s
ok      runtime/trace   28.375s
2016/05/06 15:33:20 Failed: exit status 1

[gopherbot]

CL https://golang.org/cl/22951 mentions this issue.