Currently, V8 uses the same counter to collect decoding time for both asm.js and
WASM. This separates the function decoding 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

Review-Url: https://codereview.chromium.org/2772363002
Cr-Commit-Position: refs/heads/master@{#44197}