Mark HCompareMap as having Tagged representation

BUG=chromium:346636
LOG=y
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/176923013

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19545 ce2b1a6d-e550-0410-aec6-3dcde31c8c00