Bug: unable to get adChoicesInfo from some ad-networks properly for native ads

[Liran Barsisa]

I use the adChoicesInfo in order to find their sizes, to avoid overlapping them in native ads.

https://developers.google.com/admob/android/reference/com/google/android/gms/ads/nativead/NativeAd#getAdChoicesInfo()

However, I've found that at least for Vungle/LiftOff, it just returns me null, so I can't know its size.

For now, I've added a workaround that if it's this ad-network, it's 20x20 dp. 

It's a workaround because I don't know for sure it's this size (I used an app to measure it) and I don't know if it will always appear, too.

Please fix this issue.

Sadly as many ad-networks fail to load test ads despite me following the guidelines, I don't know how many other ad-networks have this issue.

For example, for Mintegral:
https://developers.google.com/admob/android/mediation/mintegral#step_6_test_your_implementation
It says we can either use Admob test device method, and it doesn't work for me. It also says Mintegral suggests to use their own, but it doesn't explain how we can do it in Admob mediation environment... Why not add this to the adapter's code...

https://developers.google.com/admob/android/mediation/mintegral#enable_test_ads

Please fix this as well.