nacl/secretbox: add benchmarks

Initial results on an Ivy Bridge system for reference:

BenchmarkSeal8Bytes-8     	 5000000	       310 ns/op	  25.77 MB/s
BenchmarkSeal100Bytes-8   	 3000000	       599 ns/op	 166.76 MB/s
BenchmarkSeal1K-8         	 1000000	      1825 ns/op	 561.06 MB/s
BenchmarkSeal8K-8         	  100000	     10997 ns/op	 744.88 MB/s
BenchmarkOpen8Bytes-8     	 5000000	       327 ns/op	  24.39 MB/s
BenchmarkOpen100Bytes-8   	 2000000	       630 ns/op	 158.49 MB/s
BenchmarkOpen1K-8         	 1000000	      1752 ns/op	 584.21 MB/s
BenchmarkOpen8K-8         	  200000	     10420 ns/op	 786.12 MB/s

Fixes golang/go#20563

Change-Id: Iaacd9715840c1f5c7ee2459759e79c98a4b6f62a
Reviewed-on: https://go-review.googlesource.com/46039
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
1 file changed