The hard-coded threshold of five uses before a release was regressing
the Oort online benchmark, which seems to use an index buffer many
times, then change to a different range of indices, which would need
to check the system memory for index range validation.

Also add a performance regression test, and an update to the perf
runner script which checks for the most recent binary among the search
directories.

BUG=594066

Change-Id: Id09cc32fd00bff1c72cbe9b6fb7c210fd047a551
Reviewed-on: https://chromium-review.googlesource.com/339271Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>