When lowering Array.prototype.push/.pop to the fast inlined version, we
first need to ensure that all prototypes (including the Object.prototype)
are stable.

R=mvstanton@chromium.org
BUG=chromium:644689

Review-Url: https://codereview.chromium.org/2319533005
Cr-Commit-Position: refs/heads/master@{#39266}