Crosswalk: you can export game with native AdMob ads, but game will jitter (due to Chromium issues) and game will jitter while ussing AdMob banners.
CocoonJS: you can export smooth game with MoPub, but you will earn pennies because of no native AdMob ads (low fillrate, low CPC).
So as for now (and last months) there is no possibility to have smooth Android game with native AdMob ads.
Am I right?