Since the last update for construct 2 it's possible to use AdMob natively for android games (via Intel Crosswalk, not supported by cocoonJS).
What you need
Download the latest version of Construct 2 here
Download Construct 2
I've created this tutorial for my customers, so I just link to the web page. Otherwise I have to keep 2 Tutorials with the same topic up to date.
See Tutorial (Webview)
If you have questions, please send me a PM or comment on the web page. I don't get notified about replies on tutorials at scirra.