Should fix flakes like:

https://build.golang.org/log/c8da331317064227f38d5ef57ed7dba563ba1b38

--- FAIL: TestClientTimeout_h1 (0.35s)
    client_test.go:1263: timeout after 200ms waiting for timeout of 100ms
FAIL

Change-Id: I0a4dba607524e8d7a00f498e27d9598acde5d222
Reviewed-on: https://go-review.googlesource.com/33420
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>