I don't think you need to pass `cherr` in, just use a "constant" error:

```go
var ErrDropped = errors.New("raven: packet dropped")

func (client *Client) Capture(packet *Packet, captureTags map[string]string) (eventID string, cherr chan error) {
    // ...
    select {
    case client.queue <- outgoingPacket:
    default:
        outgoingPacket.cherr <- ErrDropped
        if client.DropHandler != nil {
            client.DropHandler(packet)
        }
    }
```