net/http: flaky TestTransportReuseConnection_Gzip_ContentLength

[rsc]

trybot failure in a cmd/go CL. nothing i'm changing in cmd/go could cause this.
only happened in the race builder, so maybe scheduling-sensitive.

https://storage.googleapis.com/go-build-log/00c78809/linux-amd64-race_9ed057c7.log

--- FAIL: TestTransportReuseConnection_Gzip_ContentLength (0.19s)
	transport_test.go:3411: didn't reuse connection
FAIL
FAIL	net/http	7.526s
2017/10/11 05:02:11 Failed: exit status 1

[bradfitz]

Unfortunately I've been unable to reproduce this (on linux-amd64 or linux-amd64-race), even with high -count values and various -cpu.

/cc @tombergan

[bradfitz]

I just spent some time on this again and still can't reproduce. I also looked at the git history for clues, but nothing.

Closing for now until we see it again or have more clues.