void handleDecodeError(Throwable e, Callback<Void> callback) {
    metrics.incrementMessagesDropped();
    handleError(e, "Cannot decode spans"::toString, callback);
  }
Before calling this, call {@link CollectorMetrics#incrementMessages()}, and {@link
CollectorMetrics#incrementBytes(int)}. Do not call any other metrics callbacks as those are
handled internal to this method.

@param serializedSpans not empty message
zipkin-collector/core/src/main/java/zipkin2/collector/Collector.java