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
* This method is internal to the framework; subclassers should not call
	 * this method.
	 * </p>
	 * @param widget
     *            the widget
	 * @param element
     *            the element
	 */
	protected final void refreshItem(Widget widget, Object element) {
		SafeRunnable.run(new UpdateItemSafeRunnable(widget, element, true));
	}
	/**
	 * Removes the given open listener from this viewer. Has no affect if an
	 * identical listener is not registered.
	 * 
	 * @param listener
	 *            a double-click listener
	 */
	public void removeOpenListener(IOpenListener listener) {
		openListeners.remove(listener);
	}
	/*
	 * (non-Javadoc) Method declared on IPostSelectionProvider.
	 */
	public void removePostSelectionChangedListener(ISelectionChangedListener listener) {
		postSelectionChangedListeners.remove(listener);
	}
	/**
	 * Removes the given double-click listener from this viewer. Has no affect
	 * if an identical listener is not registered.