This uses a separate temporary zone for running the asm.js parser, which
can be discarded immediately after the parser finished validating one
module. It reduces the lifetime of all data-structures local to the
parser and only uses the compilation zone to hold the resulting module.

R=clemensh@chromium.org

Change-Id: I5f5a613e0abd24cd85a49ebd97f9ee7cee46b02a
Reviewed-on: https://chromium-review.googlesource.com/506733
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45377}