Check if mtime of dependency_path is greater than stored mtime.

def check_dependency(self, dependency_path):
        """Check if mtime of dependency_path is greater than stored mtime."""
        stored_hash = self._stamp_file_hashes.get(dependency_path)

        # This file was newly added, or we don't have a file
        # with stored hashes yet. Assume out of date.
        if not stored_hash:
            return False

        return stored_hash == _sha1_for_file(dependency_path)