Currently, V8 uses the same counter to collect decoding time for both asm.js and
WASM. This separates that counter into two separate counters, and then uses the appropriate counter when instantiating a module.

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

Review-Url: https://codereview.chromium.org/2780563002
Cr-Commit-Position: refs/heads/master@{#44163}