// Stack the two children vertically, meeting at 50%.
topLayer.setLeftRight(0, PX, 0, PX);
bottomLayer.setLeftRight(0, PX, 0, PX);
topLayer.setTopHeight(0, PCT, 50, PCT);
bottomLayer.setBottomHeight(0, PCT, 50, PCT);
layout.layout();
// Update the two children to stack horizontally, meeting at 10em.
// Also have them animate for 500ms.
topLayer.setTopBottom(0, PX, 0, PX);
bottomLayer.setTopBottom(0, PX, 0, PX);