of elements is set to a safe lower bound.  Move the setting of the
static type out of VirtualFrame::MergeTo (which is not necessarily run
for all frames) and into VirtualFrame::PrepareMergeTo (which is).
Review URL: http://codereview.chromium.org/92009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1767 ce2b1a6d-e550-0410-aec6-3dcde31c8c00