Pretenure code generation corner case with new space COW arrays.

When advised to pretenure in crankshaft, and the boilerplate is a cow
array, move the elements to old space if it's not already there to avoid
overflowing the store buffer.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/197473004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19995 ce2b1a6d-e550-0410-aec6-3dcde31c8c00