Adds a couple more measures to the benchmarking app

examples/dart/mojo_rtt_benchmark/lib/main.dart

Index: examples/dart/mojo_rtt_benchmark/lib/main.dart
diff --git a/examples/dart/mojo_rtt_benchmark/lib/main.dart b/examples/dart/mojo_rtt_benchmark/lib/main.dart
index ad5cf9d3122a415fb0f5076af25d5289bcc790f0..2b79e4b09a54472f61e773c8d86bffb3f84b4f65 100644
--- a/examples/dart/mojo_rtt_benchmark/lib/main.dart
+++ b/examples/dart/mojo_rtt_benchmark/lib/main.dart
@@ -19,7 +19,7 @@ import 'package:mojo/core.dart';
 import 'package:mojom/mojo/examples/echo.mojom.dart';
 
 class EchoTracingApp extends Application {
-  static const Duration kWarmupDuration = const Duration(seconds: 1);
+  static const Duration kWarmupDuration = const Duration(seconds: 5);
   static const Duration kDelay = const Duration(microseconds: 50);
   TracingHelper _tracing;
   List<EchoProxy> _echoProxies;
@@ -92,7 +92,7 @@ class EchoTracingApp extends Application {
     return _echoProxies[idx]
         .ptr
         .echoString(s)
-        .catchError((_) => _errorHandler());
+        .catchError((e) => _errorHandler());
   }
 
   _errorHandler() {