Elements field of newly allocated JSArray could be left uninitialized in some cases (fast literal case).

BUG=340124
LOG=Y
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/152673004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19026 ce2b1a6d-e550-0410-aec6-3dcde31c8c00