Dart: Fixes rtt benchmark

benchmarks/mojo_rtt_benchmark/lib/main.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This Mojo app is a benchmark of Mojo/Dart IPC Round Trip Times.
 // It creates many proxies from a single isolate, and makes requests using those
 // proxies round-robin.
 // To run it, and the other RTT benchmarks:
 //
 // $ ./mojo/devtools/common/mojo_benchmark [--release] mojo/tools/data/rtt_benchmarks
@@ skipping 29 matching lines @@
     String echoUrl = "mojo:dart_echo_server";
     if (argResults["cpp-server"]) {
       echoUrl = "mojo:echo_server";
     }
     _numClients = int.parse(argResults["num-clients"]);
     _numActiveClients = int.parse(argResults["num-active-clients"]);
 
     // Setup the connection to the echo app.
     for (int i = 0; i < _numClients; i++) {
       var newProxy = new EchoProxy.unbound();
-      newProxy.errorFuture.then((e) {
+      newProxy.ctrl.errorFuture.then((e) {
         _errorHandler(e);
       });
       connectToService(echoUrl, newProxy);
       _echoProxies.add(newProxy);
     }
 
     // Start echoing.
     _doEcho = true;
     Timer.run(() => _run(0));
 
@@ skipping 43 matching lines @@
     return Future.wait(_echoProxies.map((p) => p.close())).then((_) {
       MojoHandle.reportLeakedHandles();
     });
   }
 }
 
 main(List args, Object handleToken) {
   MojoHandle appHandle = new MojoHandle(handleToken);
   new EchoTracingApp.fromHandle(appHandle);
 }