Bug 292322 [Viewers] Tree view is removing + indicator when one of multiple children is removed.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreeViewer.java
* {@link ILazyTreeContentProvider} interface, or (as of 3.3) the
 * {@link ILazyTreePathContentProvider}. If the content provider is an
 * <code>ILazyTreeContentProvider</code> or an
 * <code>ILazyTreePathContentProvider</code>, the underlying Tree must be
 * created using the {@link SWT#VIRTUAL} style bit, the tree viewer will not
 * support sorting or filtering, and hash lookup must be enabled by calling
 * {@link #setUseHashlookup(boolean)}.
 * </p>
 * <p>
 * Users setting up an editable tree with more than 1 column <b>have</b> to pass the
 * SWT.FULL_SELECTION style bit
 * </p>
 * @noextend This class is not intended to be subclassed by clients.
 */
public class TreeViewer extends AbstractTreeViewer {
	private static final String VIRTUAL_DISPOSE_KEY = Policy.JFACE
			+ ".DISPOSE_LISTENER"; 
	/**
	 * This viewer's control.
	 */
	private Tree tree;
	/**
	 * Flag for whether the tree has been disposed of.
	 */
	private boolean treeIsDisposed = false;
	private boolean contentProviderIsLazy;
	private boolean contentProviderIsTreeBased;
	/**
	 * The row object reused
	 */