Sort unexpected test results.

testing/tools/run_pixel_tests.py

 #!/usr/bin/env python
 # Copyright 2015 The PDFium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import optparse
 import os
 import re
 import subprocess
 import sys
@@ skipping 52 matching lines @@
     if input_file_re.match(input_filename):
       input_path = os.path.join(source_dir, input_filename)
       if os.path.isfile(input_path):
         if test_suppressor.IsSuppressed(input_filename):
           continue
         if not generate_and_test(input_filename, source_dir, working_dir,
                                  fixup_path, pdfium_test_path, image_differ):
           failures.append(input_path)
 
   if failures:
+    failures.sort()
     print '\n\nSummary of Failures:'
     for failure in failures:
       print failure
     return 1
   return 0
 
 if __name__ == '__main__':
   sys.exit(main())