To bring V8 into line with the proposed design changes in:

 https://github.com/WebAssembly/design/pull/489

R=ahaas@chromium.org,bradnelson@chromium.org
LOG=Y
BUG=chromium:575167
BUG=v8:4735

Review URL: https://codereview.chromium.org/1624323003

Cr-Commit-Position: refs/heads/master@{#33776}