@Override
    public KeyboardSelectionPolicy getKeyboardSelectionPolicy() {
        return presenter.getKeyboardSelectionPolicy();
    }
Get the index of the row that is currently selected via the keyboard,
relative to the page start index.

<p>
This is not same as the selected row in the {@link SelectionModel}. The
keyboard selected row refers to the row that the user navigated to via the
keyboard or mouse.
</p>

@return the currently selected row, or -1 if none selected
stroom-core-client-widget/src/main/java/com/google/gwt/user/cellview/client/AbstractHasData.java