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

test/mjsunit/regress/regress-crbug-158185.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 18 matching lines @@
              Object.keys(JSON.parse('{"0023456": 1}'))[0]);
 assertEquals("1234567890123",
              Object.keys(JSON.parse('{"1234567890123": 1}'))[0]);
 assertEquals("123456789ABCD",
              Object.keys(JSON.parse('{"123456789ABCD": 1}'))[0]);
 assertEquals("12A",
              Object.keys(JSON.parse('{"12A": 1}'))[0]);
 
 assertEquals(1, JSON.parse('{"0":1}')[0]);
 assertEquals(undefined, JSON.parse('{"00":1}')[0]);
-