Load elimination fix: load should not be replaced with another load if the former is not dominated by the latter.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/151333003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18985 ce2b1a6d-e550-0410-aec6-3dcde31c8c00