Fix pattern detection for replacing shifts by rotation.

BUG=2499
R=svenpanne@chromium.org

Review URL: https://chromiumcodereview.appspot.com/12047015
Patch from Hirofumi Mako <mkhrfm@gmail.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13464 ce2b1a6d-e550-0410-aec6-3dcde31c8c00