This is useful for things that don't ever change, but we don't want to
eagerly compute the result.

Doing this from the embedder is difficult, using DefineOwnProperty would
read the property to get the property descriptor, creating an endless
recursion.

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

Review-Url: https://codereview.chromium.org/2449783006
Cr-Commit-Position: refs/heads/master@{#40648}