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

test/mjsunit/string-natives.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 59 matching lines @@
   for (var i = 0; i < 1000; i++) {
     assertEquals(5000, a[i].length);
   }
 }
 
 
 test();
 test();
 %OptimizeFunctionOnNextCall(test);
 test();
-