Unrevert "Remove BinaryOp::result_type""

Reenables https://code.google.com/p/v8/source/detail?r=15265

R=jkummerow@chromium.org
BUG=

Review URL: https://codereview.chromium.org/18309005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15505 ce2b1a6d-e550-0410-aec6-3dcde31c8c00