Gather a list of proxies to use.

def _GetProxies(self):
    """Gather a list of proxies to use."""
    # Detect proxies from the OS environment.
    result = client_utils.FindProxies()

    # Also try to connect directly if all proxies fail.
    result.append("")

    # Also try all proxies configured in the config system.
    result.extend(config.CONFIG["Client.proxy_servers"])

    return result