Refactor ParseObjectLiteral

This extracts the parsing of the ObjectLiteralProperty into its own
function. This is in preparation for adding support for parsing classes.

BUG=None
LOG=Y
R=dslomov@chromium.org, marja@chromium.org

Review URL: https://codereview.chromium.org/458613004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23249 ce2b1a6d-e550-0410-aec6-3dcde31c8c00