Cleanup class parsing a bit

BUG=v8:3330
LOG=Y
R=marja@chromium.org

Review URL: https://codereview.chromium.org/575083002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24051 ce2b1a6d-e550-0410-aec6-3dcde31c8c00