Class syntax parsing

This implements parsing for ClassExpression and ClassDeclaration.
The runtime is not yet implemented and the value is currently
hard coded to undefined.

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

Review URL: https://codereview.chromium.org/561913002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23988 ce2b1a6d-e550-0410-aec6-3dcde31c8c00