1) To get proper test coverage for the flag turned off

2) We need more scope analysis in the PreParser to not disable
optimizations for some common cases (inner function "var i" shadowing
outer function vars).

R=verwaest@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2365263005
Cr-Commit-Position: refs/heads/master@{#39768}