Expose Value::IsArgumentsObject in V8 API.

R=yangguo@chromium.org, svenpanne@chromium.org, yangguo

Review URL: https://codereview.chromium.org/460333002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23105 ce2b1a6d-e550-0410-aec6-3dcde31c8c00