Make a copy of the descriptor array when copying a map with pre-allocated properties. The garbage collector assumes that no two maps point to the same descriptor array.

A simple reduction is missing.

BUG=http://crbug.com/20330
TEST=none
Review URL: http://codereview.chromium.org/177018

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2780 ce2b1a6d-e550-0410-aec6-3dcde31c8c00