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/ClipboardOperationAction.java
private static final String TYPE_NAME = "source-with-imports-transfer-format" + System.currentTimeMillis(); 
		private static final int TYPEID = registerType(TYPE_NAME);
		
		/* (non-Javadoc)
		 * @see org.eclipse.swt.dnd.Transfer#getTypeIds()
		 */
		protected int[] getTypeIds() {
			return new int[] { TYPEID };
		}
		
		/* (non-Javadoc)
		 * @see org.eclipse.swt.dnd.Transfer#getTypeNames()
		 */
		protected String[] getTypeNames() {
			return new String[] { TYPE_NAME };
		}
		/* (non-Javadoc)