Miss the barrier alignment metric for the case of two inputs

When the StreamTwoInputSelectableProcessor was introduced before, it was missing to add the barrier alignment metric in the constructor. But it does not cause problems then, because only StreamTwoInputProcessor works at that time.

After StreamTwoInputProcessor is replaced by StreamTwoInputSelectableProcessor as now, this bug is exposed and we will not see the barrier alignment metric for the case of two inputs.

The solution is to add this metric while constructing the current StreamTwoInputProcessor.