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/TreeViewer.java
* Cancels a currently active cell editor. All changes already done in the
	 * cell editor are lost.
	 * 
	 * @since 3.1
	 */
	public void cancelEditing() {
		treeViewerImpl.cancelEditing();
	}
	/*
	 * (non-Javadoc) Method declared in AbstractTreeViewer.
	 */
	protected void doUpdateItem(final Item item, Object element) {
		if (!(item instanceof TreeItem))
			return;
		TreeItem treeItem = (TreeItem) item;
		if (treeItem.isDisposed()) {
			unmapElement(element);
			return;
		}
		colorAndFontCollector.setFontsAndColors(element);
		IBaseLabelProvider prov = getLabelProvider();
		ITableLabelProvider tprov = null;
		if (prov instanceof ITableLabelProvider) {
			tprov = (ITableLabelProvider) prov;
		}
		int columnCount = tree.getColumnCount();
		if (columnCount == 0) {
								
			ViewerLabel updateLabel = new ViewerLabel(treeItem.getText(),
					treeItem.getImage());