The metadata introduced in this patch will be useful for postmortem
tools to inspect Contexts and ScopeInfos (see
https://github.com/nodejs/llnode/issues/211).

R=bmeurer@google.com, yangguo@google.com

Change-Id: I927fcab4014d128bd782046c1ecb9ee045723e95
Reviewed-on: https://chromium-review.googlesource.com/1153858Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54768}