Ensure correct line endings for method_mirror_source tests.

tests/lib/mirrors/method_mirror_source_line_ending_lf.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// This file is marked executable so source control will preserve the type of
-// line ending.
+// Note: This test relies on LF line endings in the source file.
 
 library line_endings.lf;
 
 oneLineLF(x) => x;
 multiLineLF(y) {
   return y + 1;
 }
 a
 (){
 }