This patch restores the status of rewritable expressions, which
were not considered valid variable references before CL 2126233002,
regardless of the type of the wrapped expression.

R=mstarzinger@chromium.org, verwaest@chromium.org
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2158853002
Cr-Commit-Position: refs/heads/master@{#37864}