Add Seq[One,Two]ByteString to runtime test generator.

R=dcarney@chromium.org, jkummerow@chromium.org

Review URL: https://codereview.chromium.org/303543006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21557 ce2b1a6d-e550-0410-aec6-3dcde31c8c00