This adds the --validate-asm flag which will trigger validation of all
asm.js modules before they are being compiled. In case a module doesn't
pass validation, a warning will be printed, but compilation as well as
execution will continue unhampered.

R=mvstanton@chromium.org

Review-Url: https://codereview.chromium.org/1972593002
Cr-Commit-Position: refs/heads/master@{#36216}