Add a simple microbenchmark for calling copyWithin on a moderately large
Float64Array with 10,000 elements.

BUG=v8:5925, v8:5929, v8:4648
R=cbruni@chromium.org, adamk@chromium.org, littledan@chromium.org

Review-Url: https://codereview.chromium.org/2676193002
Cr-Commit-Position: refs/heads/master@{#42944}