We still share the code globally, but if we wanted, it would be easy to
make it per isolate now

BUG=v8:2487
R=yangguo@chromium.org,jkummerow@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/1468313004

Cr-Commit-Position: refs/heads/master@{#32217}