Move ParsePostfixExpression into ParserBase.

+ enable a test which checks that Parser and PreParser produce the "invalid left
hand side" errors consistently.

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/202333004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20149 ce2b1a6d-e550-0410-aec6-3dcde31c8c00