driver: add -trace to record execution trace

This adds a -trace flag to specify a file name for recording an
execution trace of the benchmark.  This flag parallels go test -trace.

Change-Id: Ie01ca39699dea246f549212f2be78f18aa0835c9
Reviewed-on: https://go-review.googlesource.com/6830
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
1 file changed