ReturnValue::Set(uint32_t) is wrong

R=svenpanne@chromium.org
BUG=

Review URL: https://codereview.chromium.org/16365008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14990 ce2b1a6d-e550-0410-aec6-3dcde31c8c00