frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java

public Handler mKeyMouseHandler = new Handler() {
        public void handleMessage(Message msg) {
            switch(msg.what){
            case KeyEvent.KEYCODE_SYSTEM_NAVIGATION_LEFT:
++                mdeltax = -2.0f;
                mdeltay = 0;
                break;
            case KeyEvent.KEYCODE_SYSTEM_NAVIGATION_RIGHT:
++                mdeltax = 2.0f;
                mdeltay = 0;
                break;
            case KeyEvent.KEYCODE_SYSTEM_NAVIGATION_UP:
                mdeltax = 0;
++                mdeltay = -2.0f;
                break;
            case KeyEvent.KEYCODE_SYSTEM_NAVIGATION_DOWN:
                mdeltax = 0;
++                mdeltay = 2.0f;
                break;
            case KeyEvent.KEYCODE_PROFILE_SWITCH:
                mdeltax = 0;
                mdeltay = 0;
                break;
            default:
                break;
            }