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
* @param filter The new filter.
		 */
		public void setFilter(IPropertyChangeEventFilter filter) {
			fFilter= filter;
		}
		
		/**
		 * Returns the event filter.
		 * 
		 * @return The event filter.
		 */
		public IPropertyChangeEventFilter getFilter() {
			return fFilter;
		}
	}
	
	/*
	 * Link mode.  
	 */
	class MouseClickListener implements KeyListener, MouseListener, MouseMoveListener,
		FocusListener, PaintListener, IPropertyChangeListener, IDocumentListener, ITextInputListener, ITextPresentationListener {
		
		private boolean fActive;
		
		private IRegion fActiveRegion;
		
		private Position fRememberedPosition;
		
		private Cursor fCursor;