check results div below to see that before adding text, document is smaller than viewport
after adding text, document should be bigger than viewport,and check that viewport size hasn't changed,
except maybe being a little bit smaller (about 15px) because of the size of the scrollbars
resize browser window and click the "recompute size" button; reported viewport size should change
scroll the window and click "recompute size" to see that the scroll position is taken into effect