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
OverrideIndicator(boolean isOverwriteIndicator, String text, String key) {
			super(ANNOTATION_TYPE, false, text);
			fIsOverwriteIndicator= isOverwriteIndicator;
			fAstNodeKey= key;
		}
		/**
		 * Tells whether this is an overwrite or an override indicator.
		 * 
		 * @return <code>true</code> if this is an overwrite indicator
		 */
		public boolean isOverwriteIndicator() {
			return fIsOverwriteIndicator;
		}
		/**
		 * Opens and reveals the defining method.
		 */
		public void open() {
			boolean hasLogEntry= false;
			CompilationUnit ast= JavaPlugin.getDefault().getASTProvider().getAST(fJavaElement, true, null);
			ASTNode node= null;
			if (ast != null)
				node= ast.findDeclaringNode(fAstNodeKey);
			if (node instanceof MethodDeclaration) {
				try {
					IMethodBinding methodBinding= ((MethodDeclaration)node).resolveBinding();
					IMethodBinding definingMethodBinding= Bindings.findMethodDefininition(methodBinding, true);
					if (definingMethodBinding != null) {
						String definingTypeQualifiedName= definingMethodBinding.getDeclaringClass().getQualifiedName();
						IType definingType= null;
						IType type= getType(methodBinding);