Replaces the layout (after a mode, rotation or page-size change): tiles already on the surface stay valid when their page's size is unchanged. The next Update(in Viewport) or RunFrame(TimeSpan) works out the wanted tiles again.
public void SetLayout(PageLayout layout)
The new layout.
Spec #33 viewer capability 3. A remote document can show page 1 before its other pages' sizes are known: lay out placeholder sizes, then set the real layout as GetPageMetricsAsync(Int32, CancellationToken) delivers them.