This adds an early check to the graph builder which prevents adding an
HWrapReceiver instruction if the receiver type is already known at graph
building time. Also HAllocate no longer unnecessarily postpones setting
it's type until type inference but sets it right away. These changes are
in preparation for escape analysis.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/19493005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15843 ce2b1a6d-e550-0410-aec6-3dcde31c8c00