Both failed to generate a miss if the key wasn't "length".
ARM and MIPS were already correct.

BUG=v8:2566

Review URL: https://codereview.chromium.org/12378085

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13828 ce2b1a6d-e550-0410-aec6-3dcde31c8c00