- Added gating code in the module-decoder to allow SIMD code only when
 it can be decoded correctly
 - SIMD128 values should not be exported to JS
 - Try/Catch should not be available in asmjs modules
 - Trivial fixes for S128  values

BUG=chromium:648079

R=ahaas@chromium.org, titzer@chromium.org, bradnelson@chromium.org

Review-Url: https://codereview.chromium.org/2400863003
Cr-Commit-Position: refs/heads/master@{#40067}