Use std::chrono::steady_clock for benchmarks.
Use std::chrono::steady_clock for benchmarks.

Change-Id: I56072ae0454cff98fde3854e441201de3f3f7baa
Reviewed-on: https://code-review.googlesource.com/6712
Reviewed-by: Paul Wankadia <62d4e38bb1380f055ec4b899baa75e52af09c5f7@google.com>

google/re2,google/re2,google/re2,google/re2,google/re2