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/OverrideIndicatorManager.java
* Updates the override and implements annotations based
	 * on the given AST.
	 * 
	 * @param ast the compilation unit AST
	 * @param progressMonitor the progress monitor
	 * @since 3.0
	 */
	protected void updateAnnotations(CompilationUnit ast, IProgressMonitor progressMonitor) {
		
		if (ast == null || progressMonitor.isCanceled())
			return;
		
		final Map annotationMap= new HashMap(50);
		ast.accept(new ASTVisitor(false) {
			/*
			 * @see org.eclipse.jdt.core.dom.ASTVisitor#visit(org.eclipse.jdt.core.dom.MethodDeclaration)
			 */
			public boolean visit(MethodDeclaration node) {
				IMethodBinding binding= node.resolveBinding();
				if (binding != null) {
					IMethodBinding definingMethod= Bindings.findMethodDefininition(binding, true);
					if (definingMethod != null) {
						
						ITypeBinding definingType= definingMethod.getDeclaringClass();
						String qualifiedMethodName= definingType.getQualifiedName() + "." + binding.getName(); 
						
						boolean isImplements= JdtFlags.isAbstract(definingMethod);
						String text;
						if (isImplements)
							text= JavaEditorMessages.getFormattedString("OverrideIndicatorManager.implements", qualifiedMethodName);