Processes the file contents.

def ProcessContent(self, strip_expansion=False):
    """Processes the file contents."""
    self._ParseFile()
    if strip_expansion:
      # Without a collection the expansions become blank, removing them.
      collection = None
    else:
      collection = MacroCollection()
    for section in self._sections:
      section.BindMacroCollection(collection)
    result = ''
    for section in self._sections:
      result += section.text
    self._processed_content = result