Dart: Use a RawReceivePort to receive events for Mojo handles.

benchmarks/mojo_rtt_benchmark/lib/echo_server.dart

Index: benchmarks/mojo_rtt_benchmark/lib/echo_server.dart
diff --git a/benchmarks/mojo_rtt_benchmark/lib/echo_server.dart b/benchmarks/mojo_rtt_benchmark/lib/echo_server.dart
index 260836114aba5c80a670ca28465d5b153312350d..5134158830280083441adf52512240ded221da84 100644
--- a/benchmarks/mojo_rtt_benchmark/lib/echo_server.dart
+++ b/benchmarks/mojo_rtt_benchmark/lib/echo_server.dart
@@ -23,7 +23,7 @@ class EchoImpl implements Echo {
 
   Future close() => _stub.close();
 
-  _errorHandler() => _application.removeService(this);
+  _errorHandler(Object e) => _application.removeService(this);
 }
 
 class EchoApplication extends Application {
@@ -59,7 +59,7 @@ class EchoApplication extends Application {
     return echoService;
   }
 
-  _errorHandler() async {
+  _errorHandler(Object e) async {
     _closing = true;
     for (var service in _echoServices) {
       await service.close();