Bug 265856 [Viewers] TreeViewer Widget Dispose Error
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/SWTFocusCellManager.java
private CellNavigationStrategy navigationStrategy;
	private ColumnViewer viewer;
	private ViewerCell focusCell;
	private FocusCellHighlighter cellHighlighter;
	private DisposeListener itemDeletionListener = new DisposeListener() {
		public void widgetDisposed(DisposeEvent e) {
			setFocusCell(null);
		}
	};
	/**
	 * @param viewer
	 * @param focusDrawingDelegate
	 * @param navigationDelegate