R=titzer@chromium.org
TEST=mjsunit/wasm/anyref

Change-Id: Ia79c78038f6cc92f657ee1b48474323bde981155
Reviewed-on: https://chromium-review.googlesource.com/1201784Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55583}