Fix HInnerAllocatedObject to use an HValue for the offset.

R=hpayer@chromium.org, mvstanton@chromium.org

Review URL: https://codereview.chromium.org/98673003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18181 ce2b1a6d-e550-0410-aec6-3dcde31c8c00