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/internal/ui/javaeditor/JavaEditor.java
} catch (JavaModelException x) {
			JavaPlugin.log(x.getStatus());
		}
		
		ISourceViewer viewer= getSourceViewer();
		if (viewer instanceof ITextViewerExtension5) {
			ITextViewerExtension5 extension= (ITextViewerExtension5) viewer;
			extension.exposeModelRange(new Region(offset, length));
		} else {
			resetHighlightRange();
		}
	}
			
	protected boolean isActivePart() {
		IWorkbenchPart part= getActivePart();
		return part != null && part.equals(this);
	}
	private boolean isJavaOutlinePageActive() {
		IWorkbenchPart part= getActivePart();
		return part instanceof ContentOutline && ((ContentOutline)part).getCurrentPage() == fOutlinePage;
	}
	private IWorkbenchPart getActivePart() {
		IWorkbenchWindow window= getSite().getWorkbenchWindow();
		IPartService service= window.getPartService();
		IWorkbenchPart part= service.getActivePart();
		return part;
	}
	
	/*
	 * @see StatusTextEditor#getStatusHeader(IStatus)