SimpleSlice now calls [[Get]] before [[Has]] when generating copy

SparseSlice does not need this (non-optimal) reordering since its
callers guarantee that [[Get]] has no side effects on the passed-in array.

BUG=v8:3643
LOG=n
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/674003002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24884 ce2b1a6d-e550-0410-aec6-3dcde31c8c00