Bug 161738 [Undo] - API - promote ability to quietly compute status to operations API
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/ide/undo/WorkspaceUndoMonitor.java
* Get a change listener for listening to operation history changes.
	 * 
	 * @return the resource change listeners
	 */
	private IOperationHistoryListener getOperationHistoryListener() {
		return new IOperationHistoryListener() {
			/*
			 * (non-Javadoc)
			 * 
			 * @see org.eclipse.core.commands.operations.IOperationHistoryListener#historyNotification(org.eclipse.core.commands.operations.OperationHistoryEvent)
			 */
			public void historyNotification(OperationHistoryEvent event) {
				switch (event.getEventType()) {
				case OperationHistoryEvent.ABOUT_TO_EXECUTE:
				case OperationHistoryEvent.ABOUT_TO_UNDO:
				case OperationHistoryEvent.ABOUT_TO_REDO:
					operationInProgress = event.getOperation();
					break;
				case OperationHistoryEvent.DONE:
				case OperationHistoryEvent.UNDONE:
				case OperationHistoryEvent.REDONE:
					resetChangeCount();
					operationInProgress = null;
					break;
				case OperationHistoryEvent.OPERATION_NOT_OK:
					operationInProgress = null;
					break;
				}
			}
		};