Given a list of strings representing environment variables, prepend the
        environment variables corresponding to the proxy settings.

def inject_proxy_environment(self, environment):
        '''
        Given a list of strings representing environment variables, prepend the
        environment variables corresponding to the proxy settings.
        '''
        if not self:
            return environment

        proxy_env = format_environment(self.get_environment())
        if not environment:
            return proxy_env
        # It is important to prepend our variables, because we want the
        # variables defined in "environment" to take precedence.
        return proxy_env + environment