Fix python scripts in src/build/

build/extract_from_cab.py

 #!/usr/bin/env python
-# Copyright (c) 2009 The Chromium Authors. All rights reserved.
+# Copyright (c) 2011 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.
 
-# Extracts a single file from a CAB archive.
+"""Extracts a single file from a CAB archive."""
 
 import os
 import subprocess
 import sys
 
-if len(sys.argv) != 4:
-  print 'Usage: extract_from_cab.py cab_path archived_file output_dir'
-  sys.exit(1)
 
-[cab_path, archived_file, output_dir] = sys.argv[1:]
+def main():
+  if len(sys.argv) != 4:
+    print 'Usage: extract_from_cab.py cab_path archived_file output_dir'
+    return 1
 
-# Invoke the Windows expand utility to extract the file.
-level = subprocess.call(['expand', cab_path, '-F:' + archived_file, output_dir])
-if level != 0:
-  sys.exit(level)
+  [cab_path, archived_file, output_dir] = sys.argv[1:]
 
-# The expand utility preserves the modification date and time of the archived
-# file. Touch the extracted file. This helps build systems that compare the
-# modification times of input and output files to determine whether to do an
-# action.
-os.utime(os.path.join(output_dir, archived_file), None)
+  # Invoke the Windows expand utility to extract the file.
+  level = subprocess.call(
+      ['expand', cab_path, '-F:' + archived_file, output_dir])
+  if level != 0:
+    return level
+
+  # The expand utility preserves the modification date and time of the archived
+  # file. Touch the extracted file. This helps build systems that compare the
+  # modification times of input and output files to determine whether to do an
+  # action.
+  os.utime(os.path.join(output_dir, archived_file), None)
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())