Revert "Unify paren handling in Parser and PreParser."

This reverts r19140.

Reason: Octane regression.

BUG=
TBR=verwaest@chromium.org

Review URL: https://codereview.chromium.org/156673002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19147 ce2b1a6d-e550-0410-aec6-3dcde31c8c00