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
private boolean fMarkConstantOccurrences;
	/**
	 * Tells whether to mark field occurrences in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fMarkFieldOccurrences;
	/**
	 * Tells whether to mark local variable occurrences in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fMarkLocalVariableypeOccurrences;
	/**
	 * Tells whether to mark exception occurrences in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fMarkExceptionOccurrences;
	/**
	 * Tells whether to mark method exits in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fMarkMethodExitPoints;
	/**
	 * 
	 */
	private ISelection fForcedMarkOccurrencesSelection;
	/**