Instead of creating them on demand all over the place.

I plan to link ScopeInfos together, and having one place where all
ScopeInfos are created will make this easier.

R=verwaest@chromium.org,adamk@chromium.org
TBR=mstarzinger@chromium.org
BUG=v8:5215

Review-Url: https://codereview.chromium.org/2281073002
Cr-Commit-Position: refs/heads/master@{#39003}