encoding/json: use sync.Pool
Benchmark is within the noise. I had to run this a dozen times
each before & after (on wall power, without a browser running)
before I could get halfway consistent numbers, and even then
they jumped all over the place, with the new one sometimes
being better. But these are the best of a dozen each.
Slowdown is expected anyway, since I imagine channels are
optimized more.
benchmark old ns/op new ns/op delta
BenchmarkCodeEncoder
26556987 27291072 +2.76%
BenchmarkEncoderEncode 1069 1071 +0.19%
benchmark old MB/s new MB/s speedup
BenchmarkCodeEncoder 73.07 71.10 0.97x
benchmark old allocs new allocs delta
BenchmarkEncoderEncode 2 2 0.00%
benchmark old bytes new bytes delta
BenchmarkEncoderEncode 221 221 0.00%
Update #4720
R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/
37720047