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
/*
		 * @see org.eclipse.jface.text.IDocumentListener#documentChanged(org.eclipse.jface.text.DocumentEvent)
		 */
		public void documentChanged(DocumentEvent event) {
		}
		/*
		 * @see org.eclipse.jface.text.ITextInputListener#inputDocumentAboutToBeChanged(org.eclipse.jface.text.IDocument, org.eclipse.jface.text.IDocument)
		 */
		public void inputDocumentAboutToBeChanged(IDocument oldInput, IDocument newInput) {
			if (oldInput == null)
				return;
			oldInput.removeDocumentListener(this);
		}
		/*
		 * @see org.eclipse.jface.text.ITextInputListener#inputDocumentChanged(org.eclipse.jface.text.IDocument, org.eclipse.jface.text.IDocument)
		 */
		public void inputDocumentChanged(IDocument oldInput, IDocument newInput) {
			if (newInput == null)
				return;
			newInput.addDocumentListener(this);
		}
	}
	
	/**
	 * This action behaves in two different ways: If there is no current text
	 * hover, the javadoc is displayed using information presenter. If there is
	 * a current text hover, it is converted into a information presenter in
	 * order to make it sticky.
	 */
	class InformationDispatchAction extends TextEditorAction {