This fixes a corner-case where deoptimization while evaluating the
value to a __proto__ property after computed property names appeared
in an object literal, lead to environments not being in sync with
unoptimized code.

R=arv@chromium.org
TEST=mjsunit/harmony/computed-property-names-deopt

Review URL: https://codereview.chromium.org/1158443004

Cr-Commit-Position: refs/heads/master@{#28613}