private static Call.Factory getInternalClient() {
            if (internalClient == null) {
                synchronized (Factory.class) {
                    if (internalClient == null) {
                        internalClient = new OkHttpClient();
                    }
                }
            }
            return internalClient;
        }
Constructor for a new Factory that runs requests using given client.

@param client this is typically an instance of {@code OkHttpClient}.
arms/src/main/java/com/jess/arms/http/OkHttpUrlLoader.java