As the documentation strings say: The size should be a *tuple*. In
reality we so far passed a set. The problem with the set is that
ordering is not guaranteed, and hence we cannot assume the first and
second item have meaning (minimum vs. default size).
While at it, use a type annotation to catch such bugs easily.
Change-Id: I553616f8c6c4aaa8f635b3d7d94e8e8f49ed5a56
13edf30d6c