The "New Button Universe" PR, #59702, landed less than 24 hours ago. We've just been informed by Material Design spec developers that they'd really prefer to call ContainedButton ElevatedButton. In fact, when an updated Material Design spec is published, the official name will have been changed.

Since the ContainedButton class is so new, and because "ElevatedButton" is a little closer to the original "RaisedButton" name, we're going to quickly rename ContainedButton to be ElevatedButton now, and deprecate the old class names. The old classes still exist, but should be gone within a week.

I apologize for the confusion.