Tune performance test parameters.

BUG=413249
TBR=loislo@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/648243006

git-svn-id: svn://svn.chromium.org/blink/trunk@183678 bbb929c8-8fbe-4397-9dbb-9b2b20218538