This came up on an internal alias today, so I thought I would post the solution.

 The issue is when there is some code like the following:

    class BaseClass

    {

    }

    class InheritedClass : BaseClass

    {

        void SomeFunction() { }

    }

And you have a pointer to the SomeFunction function unit, how do you find out the associated base class of that function (in this case it is BaseClass).

The answer is: 

functionSymbol.EnclosingAggregateType.PrimaryBaseAggregateType