Deterministic build: more detailled comparison.

scripts/slave/recipe_modules/isolate/resources/compare_build_artifacts.py

 #!/usr/bin/env python
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 """Compare the artifacts from two builds."""
 
 import json
 import optparse
 import os
 import sys
@@ skipping 67 matching lines @@
     res += len(diff)
 
   max_filepath_len = max(len(n) for n in first_list & second_list)
   for f in sorted(first_list & second_list):
     first_file = os.path.join(first_dir, f)
     second_file = os.path.join(second_dir, f)
     files_diffs = compare_files(first_file, second_file)
     if not files_diffs:
       result = 'equal'
     else:
-      result = 'DIFFERENT: %s' % ('different size' if result == -1 else
-                                  '%d different bytes' % files_diffs)
+      file_len = os.stat(first_file).st_size
+      difference = ('different size' if result == -1 else
+                    '%d out of %d bytes are different (%.2f%%)' %
+                    (files_diffs, file_len, 100.0 * files_diffs / file_len))
+      result = 'DIFFERENT: %s' % difference
       res += 1
     print('%-*s: %s' % (max_filepath_len, f, result))
 
   print '%d files are equal, %d are different.'  % (
       len(first_list & second_list) - res, res)
 
   return 0 if res == 0 else 1
 
 
 def main():
   parser = optparse.OptionParser(usage='%prog [options]')
   parser.add_option('--first-build-dir', help='The first build directory.')
   parser.add_option('--second-build-dir', help='The second build directory.')
   options, _ = parser.parse_args()
 
   if not options.first_build_dir:
     parser.error('--first-build-dir is required')
   if not options.second_build_dir:
     parser.error('--second-build-dir is required')
 
   return compare_build_artifacts(options.first_build_dir,
                                  options.second_build_dir)
 
 
 if __name__ == '__main__':
   sys.exit(main())