This has no measurable impact on performance, but somewhat simplifies
the code.

updates #18177

name                  old time/op    new time/op    delta
EndToEnd                54.3µs ±10%    55.7µs ±12%    ~     (p=0.505 n=8+8)
EndToEnd-6              31.4µs ± 9%    32.7µs ± 6%    ~     (p=0.130 n=8+8)
EndToEnd-48             25.5µs ±12%    26.4µs ± 6%    ~     (p=0.195 n=8+8)
EndToEndHTTP            53.7µs ± 8%    51.2µs ±15%    ~     (p=0.463 n=7+8)
EndToEndHTTP-6          30.9µs ±18%    31.2µs ±14%    ~     (p=0.959 n=8+8)
EndToEndHTTP-48         24.9µs ±11%    25.7µs ± 6%    ~     (p=0.382 n=8+8)
EndToEndAsync           23.6µs ± 7%    24.2µs ± 6%    ~     (p=0.383 n=7+7)
EndToEndAsync-6         21.0µs ±23%    22.0µs ±20%    ~     (p=0.574 n=8+8)
EndToEndAsync-48        22.8µs ±16%    23.3µs ±13%    ~     (p=0.721 n=8+8)
EndToEndAsyncHTTP       25.8µs ± 7%    24.7µs ±14%    ~     (p=0.161 n=8+8)
EndToEndAsyncHTTP-6     22.1µs ±19%    22.6µs ±12%    ~     (p=0.645 n=8+8)
EndToEndAsyncHTTP-48    22.9µs ±13%    22.1µs ±20%    ~     (p=0.574 n=8+8)

name                  old alloc/op   new alloc/op   delta
EndToEnd                  320B ± 0%      321B ± 0%    ~     (p=1.000 n=8+8)
EndToEnd-6                320B ± 0%      321B ± 0%  +0.20%  (p=0.037 n=8+7)
EndToEnd-48               326B ± 0%      326B ± 0%    ~     (p=0.124 n=8+8)
EndToEndHTTP              320B ± 0%      320B ± 0%    ~     (all equal)
EndToEndHTTP-6            320B ± 0%      321B ± 0%    ~     (p=0.077 n=8+8)
EndToEndHTTP-48           324B ± 0%      324B ± 0%    ~     (p=1.000 n=8+8)
EndToEndAsync             227B ± 0%      227B ± 0%    ~     (p=0.154 n=8+7)
EndToEndAsync-6           226B ± 0%      226B ± 0%    ~     (all equal)
EndToEndAsync-48          230B ± 1%      229B ± 1%    ~     (p=0.072 n=8+8)
EndToEndAsyncHTTP         227B ± 0%      227B ± 0%    ~     (all equal)
EndToEndAsyncHTTP-6       226B ± 0%      226B ± 0%    ~     (p=0.400 n=8+7)
EndToEndAsyncHTTP-48      228B ± 0%      228B ± 0%    ~     (p=0.949 n=8+6)

name                  old allocs/op  new allocs/op  delta
EndToEnd                  9.00 ± 0%      9.00 ± 0%    ~     (all equal)
EndToEnd-6                9.00 ± 0%      9.00 ± 0%    ~     (all equal)
EndToEnd-48               9.00 ± 0%      9.00 ± 0%    ~     (all equal)
EndToEndHTTP              9.00 ± 0%      9.00 ± 0%    ~     (all equal)
EndToEndHTTP-6            9.00 ± 0%      9.00 ± 0%    ~     (all equal)
EndToEndHTTP-48           9.00 ± 0%      9.00 ± 0%    ~     (all equal)
EndToEndAsync             8.00 ± 0%      8.00 ± 0%    ~     (all equal)
EndToEndAsync-6           8.00 ± 0%      8.00 ± 0%    ~     (all equal)
EndToEndAsync-48          8.00 ± 0%      8.00 ± 0%    ~     (all equal)
EndToEndAsyncHTTP         8.00 ± 0%      8.00 ± 0%    ~     (all equal)
EndToEndAsyncHTTP-6       8.00 ± 0%      8.00 ± 0%    ~     (all equal)
EndToEndAsyncHTTP-48      8.00 ± 0%      8.00 ± 0%    ~     (all equal)

https://perf.golang.org/search?q=upload:20170428.2

Change-Id: I8ef7f71a7602302aa78c144327270dfce9211539
Reviewed-on: https://go-review.googlesource.com/42112
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>