添加到了EventEntry.java：

Added this to EventEntry.java:

@Key("@gd:etag")
public String etag;

添加到了CalendarClient.java：

Added this to CalendarClient.java:

   public void executeDelete(Entry entry) throws IOException {
        HttpRequest request = requestFactory.buildDeleteRequest(new GenericUrl(entry.getEditLink()));
        if (entry instanceof EventEntry) {
            request.headers.ifMatch = ((EventEntry) entry).etag;
        }
        request.execute().ignore();
    }