路径：frameworks/base/packages/SystemUI/src/com/android/systemui/settings/BrightnessDialog.java

由于对话框是一个Activity， finish 可以让界面销毁掉，再做个计时判断就可以了。

@Override
    protected void onStart() {
        super.onStart();
        mBrightnessController.registerCallbacks();
        MetricsLogger.visible(this, MetricsEvent.BRIGHTNESS_DIALOG);
        //三秒后自动关闭
        Handler handler = new Handler();
            handler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    finish();
                }
            },3000);
    }