Back in March, Google introduced a new rounded square icon requirement for the Google Play Store on Android and Chrome OS. App developers can choose to enable the new icon specification immediately, with the Google Contacts listing already featuring the updated style.
The goal is to "bring consistency and a cleaner look to Google Play" on different UI layouts, form factors, and devices. It prohibits transparent backgrounds, with Google dynamically adding rounded corners and drop shadows to icons. This applies to the Play Store on Android phones and tablets, as well as Chromebooks.