code: def add_extension(self, extension):
          
          if extension:
              extension_to_add = os.path.abspath(os.path.expanduser(extension))
              if os.path.exists(extension_to_add):
                  self._extension_files.append(extension_to_add)
              else:
                  raise IOError("Path to the extension doesn't exist")
          else:
              raise ValueError("argument can not be null")
docs: Adds the path to the extension to a list that will be used to extract it
          to the ChromeDriver
  
          :Args:
           - extension: path to the \\*.crx file