Reland^2 "Enable loads and stores to global vars through property cell shortcuts...

Reland^2 "Enable loads and stores to global vars through property cell shortcuts installed into parent script context".

This reverts commit 362b378501ac2220655e16f49c6d1aa734e657f4.

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/1254723004

Cr-Commit-Position: refs/heads/master@{#29849}