Give uses within a loop a greater weight when doing representation inference.

Give uses within a loop a greater weight when doing representation inference.

Uses of a value are weighted by a factor of FLAG_loop_weight (default: 10) for
every loop they are in. This makes uses in inner loops "more important", which
should improve the result of the representation inference.

Review URL: https://chromiumcodereview.appspot.com/8277031

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10573 ce2b1a6d-e550-0410-aec6-3dcde31c8c00