Also, less efficient code was generated because of negative keyed load
offsets. I changed this to benefit from HLoadKeyed dehoisting.

BUG=v8:3185
LOG=N
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/184103004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19846 ce2b1a6d-e550-0410-aec6-3dcde31c8c00