int pageHeightPadding() {
		return ((getMeasuredHeight() - pageHeight) / 2);
	}
Gets the value that getScrollX() should return if the specified page is
the current page (and no other scrolling is occurring). Use this to pass
a value to scrollTo(), for example.

@param whichPage
@return
app/src/main/java/pro/alexzaitsev/freepager/library/view/core/VerticalPager.java