There are two specific examples in the Android Floating Action Button guidelines that explain how the button can morph into either new buttons, or a toolbar.
If the hallmark of the app is adding file types, a floating action button can morph into related actions after it is first touched.
If a floating action button morphs into a toolbar, that toolbar should contain related actions. In this example, the button lets the user select the media type to add.
After the button has morphed, how does the user revert back to the previous single button mode?
As I understand it, the rest of the UI is not blocked after these buttons have morphed, so it's not clear how the user can hide the new buttons or revert the morphed shape if they decide not to go through with the new action.
This is more commentary than anything else: I just took a look at Drive to find implementation examples and found an Bottom sheet instead of a FAB morph.