Using a 256-byte buffer avoids 99% of allocations across v8's top25
benchmark. This also leads to a significant performance increase on
speedometer, with a ~1.2% improvement on jQuery, ~1.3% on VanillaJS
and an overall ~0.4% improvement on the score.

Bug: v8:7555
Change-Id: Icd6fa07341eb989892431cb1e4995557e35c7a67
Reviewed-on: https://chromium-review.googlesource.com/971837
Commit-Queue: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52125}