This CL replaces the last usages of std::vector in the AsmJsParser by
ZoneVector. This allows to also measure the memory consumption of these
vectors, since it is now contained in the zone memory.
ZoneVectors are reused to avoid accumulating lots of unused memory.

This also saves 2.6% performance (avg over 1000 runs) on my local
workstation.

R=mstarzinger@chromium.org

Change-Id: I04c96db558d9c362b1494ddd9e975edf2783403c
Reviewed-on: https://chromium-review.googlesource.com/516985Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45591}