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/SemanticHighlightingReconciler.java
* @param offset The range offset
		 * @param length The range length
		 */
		private void retainPositions(int offset, int length) {
			
			for (int i= 0, n= fRemovedPositions.size(); i < n; i++) {
				HighlightedPosition position= (HighlightedPosition) fRemovedPositions.get(i);
				if (position != null && position.isContained(offset, length)) {
					fRemovedPositions.set(i, null);
					fNOfRemovedPositions--;
				}
			}
		}
	}
	
	
	private PositionCollector fCollector= new PositionCollector();
	
	
	private JavaEditor fEditor;
	
	private ISourceViewer fSourceViewer;
	
	private SemanticHighlightingPresenter fPresenter;
	
	private SemanticHighlighting[] fSemanticHighlightings;
	
	private Highlighting[] fHighlightings;