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

test/mjsunit/regress/regress-298269.js

 // Copyright 2013 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 24 matching lines @@
   return g;
 }
 
 var s1 = "long string to make cons string 1";
 var s2 = "long string to make cons string 2";
 Cb(s1 + s2);
 Cb(s1);
 var s3 = "string for triggering osr in Cb";
 for (var i = 0; i < 16; i++) s3 = s3 + s3;
 Cb(s3);
-Cb(s1 + s2);
+Cb(s1 + s2);