Shazam has updated their Android, now allowing you to instantly buy music from Google Play directly from the app. You can also simply preview the song in Google Play if you want.
All you need to do is identify the song, and hit the new "Listen in Google Play" button. You can choose to preview the song, purchase it from Google, or listen using Google Play All Access. You can download the update from the Google Play Store right now and check it out.