private int lineCommentEnd(int start) {
    assert s.charAt(start) == '/' && s.charAt(start + 1) == '/';
    int end = s.indexOf('\n', start + 2);
    assert end > 0;
    return end;
  }
Returns the position at which this token ends and the next token begins.
value/src/main/java/com/google/auto/value/processor/JavaScanner.java