install system app

1. add permission

/frameworks/base/data/etc/oobe.xml /frameworks/base/data/etc/privapp-permissions-platform.xml

2. sign apk tools all from rom source code java -Djava.library.path=. -jar signapk.jar platform.x509.pem platform.pk8 ./app-debug.apk ./app-debug-sign.apk

3. android:sharedUserId="android.uid.system"

4. fullscreen, immersive = toggleFreeformWindowingMode & hide natvigation/statusbar /frameworks/base/core/java/com/android/internal/policy/DecorView.java

    setSystemUiVisibility(
        View.SYSTEM_UI_FLAG_IMMERSIVE
                // Set the content to appear under the system bars so that the
                // content doesn't resize when the system bars hide and show.
                | View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                // Hide the nav bar and status bar
                | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_FULLSCREEN
                | View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR);

    public void toggleFreeformWindowingMode(){
        Window.WindowControllerCallback callback = mWindow.getWindowControllerCallback();
        final int windowingMode =
                getResources().getConfiguration().windowConfiguration.getWindowingMode();
        try {
            if (windowingMode == WINDOWING_MODE_FREEFORM && callback != null) {
                callback.toggleFreeformWindowingMode();
                updateDecorCaptionShade();
            } else if (windowingMode != WINDOWING_MODE_FREEFORM && callback != null) {
                callback.toggleFreeformWindowingMode();
                updateDecorCaptionShade();
            }
        } catch (RemoteException ex) {
            Log.e(TAG, "Catch exception when process F11", ex);
        }
    }