WASM exported functions have additional internal fields which change the instance
size. Adding a getter or setter to such an exported function results in its map
becoming normalized. The normalized map cache, however, finds a different map
with a different instance size, and thus BOOM.

R=verwaest@chromium.org,cbruni@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2554343002
Cr-Commit-Position: refs/heads/master@{#41691}