Bug 89971 [Viewers] Viewers that use IViewerLabelProvider do too many instanceof checks
M6 Checking our viewer the calls to buildLabel are doing too many instanceof checks. As a result certain viewers (such as the table viewer) are twice as slow as they were in 3.0 due to these checks. I have written some performance suites to test the Table, Tree, List and Combo viewers. Table and Tree have this issue.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java
*            the element
	 * @param item
	 *            the widget
	 */
	protected void associate(Object element, Item item) {
		Object data = item.getData();
		if (data != element) {
			if (data != null)
				disassociate(item);
			item.setData(element);
		}
		
		
		
		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);