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
/**
	 * Returns the most narrow java element including the given offset.
	 * 
	 * @param offset the offset inside of the requested element
	 * @return the most narrow java element
	 */
	abstract protected IJavaElement getElementAt(int offset);
	
	/**
	 * Returns the java element of this editor's input corresponding to the given IJavaElement.
	 * 
	 * @param element the java element
	 * @return the corresponding Java element
	 */
	abstract protected IJavaElement getCorrespondingElement(IJavaElement element);
	
	/**
	 * Sets the input of the editor's outline page.
	 * 
	 * @param page the Java outline page
	 * @param input the editor input
	 */
	abstract protected void setOutlinePageInput(JavaOutlinePage page, IEditorInput input);
	
	
	/**
	 * Default constructor.
	 */
	public JavaEditor() {
		super();