The base class for all asset type-specific context menu commands is FAssetTypeActions_Base, so we need to inherit from that class.
FAssetTypeActions_Base is an abstract class that defines a number of virtual functions that allow us to extend the context menu. The interface that contains the original information for these virtual functions can be found in IAssetTypeActions.h.
We also declare a function that we bind to our custom context menu entry.
IAssetTypeActions::HasActions ( const TArray<UObject*>& InObjects ) is the function that's called by the engine code to see if our AssetTypeActions class contains any actions that can be applied to the selected objects.
IAssetTypeActions::GetActions(const TArray<UObject*>& InObjects, ...