When ExternalDragDropsOnEnter and CanInsertObjects are true, this method calls DoExternalDrop to create new objects in the document and then starts a GoToolDragging tool to allow the user to get customized feedback during the external drag into this view. When ExternalDragDropsOnEnter is false, or when the call to DoExternalDrop does not produce newly created objects in the Selection, this calls GetExternalDragImage to produce an object that is added to the view (not to the document) and appears to be dragged around by the user during the dragging-in operation.