Before we would compute the flag by iterating over all uses. The truncating 
flag is always determined at construction time since we already computed
the flag for all other instructions before inserting HChange instructions.

 
Review URL: http://codereview.chromium.org/6615012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7047 ce2b1a6d-e550-0410-aec6-3dcde31c8c00