anchor.diff:        Future pending;
         if (!_inFlightRequests.containsKey(request)) {
           var completer = new Completer();
  +        trace.record(new MultiplexerRpcSendEvent());
           var sub = _delegate.handle(request, trace).listen(completer.complete)
             ..onError(completer.completeError);
           var cancel = () {
  +          trace.record(new MultiplexerRpcCancelEvent());
             // The pending future will never complete.
             sub.cancel();
   
  
positive.code:   }
  }
  
  class MultiplexerCacheHit implements TraceEvent {
    const MultiplexerCacheHit();
  
    String toString() => 'streamy.multiplexer.cache.hit';
  }
  
  class MultiplexerCacheMiss implements TraceEvent {
    const MultiplexerCacheMiss();
  
    String toString() => 'streamy.multiplexer.cache.miss';
  }
  
  /// A [RequestHandler] which wraps [Multiplexer] and adds a few
  /// utility methods to delegate to it.
  
negative.code:       .then((cached) {
          // If there actually was an entity response, send it to the client.
          if (cached != null) {
            trace.record(new MultiplexerCacheHitEvent());
            active.submit(new Response(cached.entity, Source.CACHE, cached.ts));
          } else {
            trace.record(new MultiplexerCacheMissEvent());
          }
          var ts = new DateTime.now().millisecondsSinceEpoch;  // TODO: not testable
          // If we don't need to issue an rpc
  