Fix performance regression in regular expressions after Array.push() optimizations

R=yangguo@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/281953002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21348 ce2b1a6d-e550-0410-aec6-3dcde31c8c00