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
* current caret location are automatically marked in
	 * this editor.
	 * @since 3.0
	 */
	private boolean fMarkOccurrenceAnnotations;
	/**
	 * Tells whether the occurrence annotations are sticky
	 * i.e. whether they stay even if there's no valid Java
	 * element at the current caret position.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fStickyOccurrenceAnnotations;
	/**
	 * Tells whether to mark type occurrences in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fMarkTypeOccurrences;
	/**
	 * Tells whether to mark method occurrences in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fMarkMethodOccurrences;
	/**
	 * Tells whether to mark constant occurrences in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */