Bug 75711 AstProvider should not create AST if requested by SelectionListenerWithASTManager
3.1 M2 If SelectionListenerWithASTManager waits for an AST and the editor closes we should not create an AST for that one but return null instead.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/OverrideIndicatorLabelDecorator.java
import org.eclipse.jdt.core.dom.SimpleName;
import org.eclipse.jdt.internal.corext.dom.Bindings;
import org.eclipse.jdt.internal.corext.dom.NodeFinder;
import org.eclipse.jdt.internal.corext.util.JavaModelUtil;
import org.eclipse.jdt.internal.corext.util.JdtFlags;
import org.eclipse.jdt.internal.corext.util.SuperTypeHierarchyCache;
import org.eclipse.jdt.internal.ui.JavaPlugin;
import org.eclipse.jdt.internal.ui.JavaPluginImages;
import org.eclipse.jdt.internal.ui.viewsupport.ImageDescriptorRegistry;
import org.eclipse.jdt.internal.ui.viewsupport.ImageImageDescriptor;
/**
 * LabelDecorator that decorates an method's image with override or implements overlays.
 * The viewer using this decorator is responsible for updating the images on element changes.
 * 
 * <p>
 * This class may be instantiated; it is not intended to be subclassed.
 * </p>
 * 
 * @since 2.0
 */
public class OverrideIndicatorLabelDecorator implements ILabelDecorator, ILightweightLabelDecorator {
	private ImageDescriptorRegistry fRegistry;
	private boolean fUseNewRegistry= false;
	/**
	 * Creates a decorator. The decorator creates an own image registry to cache
	 * images. 
	 */
	public OverrideIndicatorLabelDecorator() {
		this(null);
		fUseNewRegistry= true;