Currently, V8 uses the same counter to measue module decoding peak memory bytes
for both asm.js and WASM. This CL separates the counter into two separate
counters, and then uses the appropriate counter when decoding a module.

BUG=chromium:704922
R=bbudge@chromium.org,bradnelson@chromium.org,mtrofin@chromium.org

Review-Url: https://codereview.chromium.org/2778973003
Cr-Commit-Position: refs/heads/master@{#44207}