Bug 135284 [Viewers] API: need to add methods to StructuredViewer to support ViewerComparator
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java
mapElement(element, item);
	}
	/**
	 * Disassociates the given SWT item from its corresponding element. Sets the
	 * item's data to <code>null</code> and removes the element from the
	 * element map (if enabled).
	 * 
	 * @param item
	 *            the widget
	 */
	protected void disassociate(Item item) {
		Object element = item.getData();
		Assert.isNotNull(element);
		
		unmapElement(element, item);
		item.setData(null);
	}
	/**
	 * Returns the widget in this viewer's control which represents the given
	 * element if it is the viewer's input.
	 * <p>
	 * This method is internal to the framework; subclassers should not call
	 * this method.
	 * </p>
	 * 
	 * @param element
	 * @return the corresponding widget, or <code>null</code> if none
	 */
	protected abstract Widget doFindInputItem(Object element);