In this project ad manager ad loads over the webview, and the ad displaying callback is passed from the webview through javascript interface.
goto github.com/googleads/googleads-mobile-android-examples/tree/master/java
https://stackoverflow.com/questions/10389572/call-java-function-from-javascript-over-android-webview
This is just a test app to demonstrate that aommunication between native app and webview can handle through javascript interface.
Here is the compiled apk file to run the app on your device https://drive.google.com/file/d/1k7bSp6ob3jqBAjwUQzKslhubDOV1op_F/view?usp=sharing