Bug 93400 LTK UI should provide official API for structural content in the preview page
org.eclipse.ltk.ui.refactoring/src/org/eclipse/ltk/internal/ui/refactoring/ChangeElementTreeViewer.java
protected void revealPrevious() {
		revealElement(false);
	}
	
	private void setSubtreeGrayed(Object element, boolean grayed) {
		Widget widget= findItem(element);
		if (widget instanceof TreeItem) {
			TreeItem item= (TreeItem)widget;
			if (item.getGrayed() != grayed) {
				item.setGrayed(grayed);
				grayChildren(getChildren(item), grayed);
			}
		}
	}
	
	private void grayChildren(Item[] items, boolean grayed) {
		for (int i= 0; i < items.length; i++) {
			Item element= items[i];
			if (element instanceof TreeItem) {
				TreeItem item= (TreeItem)element;
				if (item.getGrayed() != grayed) {
					item.setGrayed(grayed);
					grayChildren(getChildren(item), grayed);
				}
			}
		}
	}
	
	private void revealElement(boolean next) {