These benchmarks are only for functions commonly used in loops. The
other functions are typically used for inspection or setup and thus are
not performance sensitive.

Change-Id: I8d0a0ba2d8234ecacb40fa3aa9077bf93c8fe89c
Reviewed-on: https://go-review.googlesource.com/3680Reviewed-by: Dmitry Vyukov <dvyukov@google.com>