ArrayConcat regression recover after r20312 (appeared on dromaeo benchmarks).

BUG=chromium:358561
LOG=N
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/597103003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24269 ce2b1a6d-e550-0410-aec6-3dcde31c8c00