[Android] Implement onShowCustomView and add test case.

1. Implement onShowCustomView with requested orientation.
2. Add test case for onShow/HideCustomView.
Yes, 8-space indent is valid. I do not find an example so far, maybe
```
if (requestedOrientation != orientation &&
        requestedOrientation >= ActivityInfo.SCREEN_ORIENTATION_UNSPECIFIED &&
        requestedOrientation <= ActivityInfo.SCREEN_ORIENTATION_LOCKED) {
```
```