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

test/mjsunit/regress/regress-crbug-18639.js

 // Copyright 2009 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 17 matching lines @@
 // See http://crbug.com/18639
 
 try {
   toString = toString;
   __defineGetter__("z", (0).toLocaleString);
   z;
   z;
   ((0).toLocaleString)();
 } catch (e) {
   assertInstanceof(e, TypeError);
-}
+}