Some fixes for Swarming bots

infra/bots/win_toolchain_utils.py

 #!/usr/bin/env python
 #
 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 
 """Utilities for manipulating the win_toolchain.json file."""
 
 
 import json
+import os
+import stat
 
 
 PLACEHOLDER = '<(TOOLCHAIN_BASE_DIR)'
 
 
 def _replace_prefix(val, before, after):
   """Replace the given prefix with the given string."""
   if val.startswith(before):
     return val.replace(before, after, 1)
   return val
 
 
 def _replace(val, before, after):
   """Replace occurrences of one string with another within the data."""
   if isinstance(val, basestring):
     return _replace_prefix(val, before, after)
   elif isinstance(val, (list, tuple)):
     return [_replace(elem, before, after) for elem in val]
   elif isinstance(val, dict):
     return {_replace(k, before, after):
             _replace(v, before, after) for k, v in val.iteritems()}
   raise Exception('Cannot replace variable: %s' % val)
 
 
 def _replace_in_file(filename, before, after):
   """Replace occurrences of one string with another within the file."""
+  # Make the file writeable, or the below won't work.
+  os.chmod(filename, stat.S_IWRITE)
+
   with open(filename) as f:
     contents = json.load(f)
   new_contents = _replace(contents, before, after)
   with open(filename, 'w') as f:
     json.dump(new_contents, f)
 
 
 def abstract(win_toolchain_json, old_path):
   """Replace absolute paths in win_toolchain.json with placeholders."""
   _replace_in_file(win_toolchain_json, old_path, PLACEHOLDER)
 
 
 def resolve(win_toolchain_json, new_path):
   """Replace placeholders in win_toolchain.json with absolute paths."""
   _replace_in_file(win_toolchain_json, PLACEHOLDER, new_path)