Fix for bug 245480. Calling new Array(a) with a single argument could result in creating a holey array with a packed elements kind.

BUG=245480
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/16341004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15095 ce2b1a6d-e550-0410-aec6-3dcde31c8c00