@Override
    public CharSequence flatten(int logLevel, String tag, String message) {
        return flatten(System.currentTimeMillis(), logLevel, tag, message);
    }
Simply join the timestamp, log level, tag and message together.

@since 1.3.0
android/android_framework/base/src/main/java/com/elvishew/xlog/flattener/DefaultFlattener.java