Bug 156883 [Viewers] enhancements to ILazyTreeContentProvider
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
removeAll = true;
			addDummy = needsPlus;
			
			setExpanded(item, false);
		}
		if (removeAll) {
			
			Item[] items = getItems(item);
			for (int i = 0; i < items.length; i++) {
				if (items[i].getData() != null) {
					disassociate(items[i]);
				}
				items[i].dispose();
			}
		}
		if (addDummy) {
			newItem(item, SWT.NULL, -1); 
		}
	}
	/**
	 * Gets the expanded elements that are visible to the user. An expanded
	 * element is only visible if the parent is expanded.
	 * 
	 * @return the visible expanded elements
	 * @since 2.0
	 */
	public Object[] getVisibleExpandedElements() {
		ArrayList v = new ArrayList();
		internalCollectVisibleExpanded(v, getControl());
		return v.toArray();