Currently, V* uses the same size counter to measure the maximum number
of memory pages allocated by a module for both asm.js and WASM. This
CL separates the counter into two separate counters, and then uses the
appropriate counter when measuring.

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

Review-Url: https://codereview.chromium.org/2783713002
Cr-Commit-Position: refs/heads/master@{#44210}