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
* If <code>setSelection</code> is called from within
		 * <code>preserveSelection</code>, the call to
		 * <code>updateSelection</code> is delayed until the end of
		 * <code>preserveSelection</code>.
		 * </p>
		 * <p>
		 * Subclasses do not typically override this method, but implement
		 * <code>setSelectionToWidget</code> instead.
		 * </p>
		 */
		Control control = getControl();
		if (control == null || control.isDisposed()) {
			return;
		}
		if (!inChange) {
			setSelectionToWidget(selection, reveal);
			ISelection sel = getSelection();
			updateSelection(sel);
			firePostSelectionChanged(new SelectionChangedEvent(this, sel));
		} else {
			restoreSelection = false;
			setSelectionToWidget(selection, reveal);
		}
	}
	/**
	 * Parlays the given list of selected elements into selections on this
	 * viewer's control.
	 * <p>
	 * Subclasses should override to set their selection based on the given list
	 * of elements.