Set output representation of HIsStringAndBranch to tagged.

BUG=chromium:421877
LOG=N
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/641313003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24521 ce2b1a6d-e550-0410-aec6-3dcde31c8c00