Reduce need to augment production code to make recyclerview more testable

Is this suggested best practice or can we fix this sample to provide better ways of interacting with RecyclerViews and making assertions on the viewholder?

```
@Override
public void onBindViewHolder(ViewHolder viewHolder, final int position) {
if (position == mDataSet.size() / 2 /* calculate middle element position */) {
viewHolder.setIsInTheMiddle(true);
viewHolder.getTextView().setText(mContext.getResources().getString(R.string.middle));
} else {
viewHolder.setIsInTheMiddle(false);
viewHolder.getTextView().setText(mDataSet.get(position));
}
}
```

From : https://github.com/googlesamples/android-testing/blob/master/ui/espresso/RecyclerViewSample/app/src/androidTest/java/com/example/android/testing/espresso/RecyclerViewSample/RecyclerViewSampleTest.java

Start with RecyclerViewSampleTest.java in the linked androidTest sample and review the onBindViewHolder implementation shown in the issue. Determine whether the sample can expose better RecyclerView interactions and ViewHolder assertions without augmenting production code; done means the tests demonstrate that approach clearly.

索引モデルが issue の本文から書いたものです。