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
public void createPartControl(Composite parent) {
		super.createPartControl(parent);
		ProjectionViewer projectionViewer= (ProjectionViewer) getSourceViewer();
		
		fProjectionSupport= new ProjectionSupport(projectionViewer, getAnnotationAccess(), getSharedColors());
		fProjectionSupport.addSummarizableAnnotationType("org.eclipse.ui.workbench.texteditor.error"); 
		fProjectionSupport.addSummarizableAnnotationType("org.eclipse.ui.workbench.texteditor.warning"); 
		fProjectionSupport.setHoverControlCreator(new IInformationControlCreator() {
			public IInformationControl createInformationControl(Shell shell) {
				return new CustomSourceInformationControl(shell, IDocument.DEFAULT_CONTENT_TYPE);
			}
		});
		fProjectionSupport.install();
		
		fProjectionModelUpdater= JavaPlugin.getDefault().getFoldingStructureProviderRegistry().getCurrentFoldingProvider();
		if (fProjectionModelUpdater != null)
			fProjectionModelUpdater.install(this, projectionViewer);
				
		if (isFoldingEnabled())
			projectionViewer.doOperation(ProjectionViewer.TOGGLE);
		
		IInformationControlCreator informationControlCreator= new IInformationControlCreator() {
			public IInformationControl createInformationControl(Shell shell) {
				boolean cutDown= false;
				int style= cutDown ? SWT.NONE : (SWT.V_SCROLL | SWT.H_SCROLL);
				return new DefaultInformationControl(shell, SWT.RESIZE, style, new HTMLTextPresenter(cutDown));
			}
		};
		fInformationPresenter= new InformationPresenter(informationControlCreator);
		fInformationPresenter.setSizeConstraints(60, 10, true, true);