Bug 159190 [Viewers] multiple dispose listeners for elements in VIRTUAL tree viewer
3.3 Each time an element is mapped in a VIRTUAL tree viewer, a dispose listener is hooked to its item to properly unmap it. However, elements are mapped to the same item more than once (each time it is updated via doUpdateItem(Widget widget, Object element, boolean fullMap)). This results in many dispose listeners for each element to unmap it, which is a potential performance issue. The debugger subclasses the tree viewer and updates (clears) filtered children when an element is unmapped. It ends up doing the operation many times (once for each dispose callback), instead of once.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreeViewer.java
*/
	protected int getItemCount(Control widget) {
		return ((Tree) widget).getItemCount();
	}
	/*
	 * (non-Javadoc) Method declared in AbstractTreeViewer.
	 */
	protected int getItemCount(Item item) {
		return ((TreeItem) item).getItemCount();
	}
	/*
	 * (non-Javadoc) Method declared in AbstractTreeViewer.
	 */
	protected Item[] getItems(Item item) {
		return ((TreeItem) item).getItems();
	}
	/**
	 * The tree viewer implementation of this <code>Viewer</code> framework
	 * method ensures that the given label provider is an instance of either
	 * <code>ITableLabelProvider</code> or <code>ILabelProvider</code>. If
	 * it is an <code>ITableLabelProvider</code>, then it provides a separate
	 * label text and image for each column. If it is an
	 * <code>ILabelProvider</code>, then it provides only the label text and
	 * image for the first column, and any remaining columns are blank.
	 */
	public IBaseLabelProvider getLabelProvider() {
		return super.getLabelProvider();
	}
	/*
	 * (non-Javadoc) Method declared in AbstractTreeViewer.