A recent update to the Google Classroom Android App allows teachers to use a built-in random name selector to pick names from your class roster and keep track of who has been called on.
To use the feature, simply open the Google Classroom Android App on your mobile device - select the class from the list - select "people" at the bottom of the screen - click on the random name selector at the top of the page. From here teachers can call on the selected student by clicking next, mark a student as absent, or skip the selected student by choosing later. Check out the demo below.