Make sure files end with exactly one new line and police this in presubmit.

test/mjsunit/regress/regress-2172.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 14 matching lines @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 for (var i = 0; i < 10000; i++){
   (i + "\0").split(/(.)\1/i);
 }
 
 for (var i = 0; i < 10000; i++){
   (i + "\u1234\0").split(/(.)\1/i);
 }
-