Dart: Simplifies the handle watcher. Various cleanups and bugfixes.

mojo/dart/embedder/test/dart_to_cpp_tests.dart

Index: mojo/dart/embedder/test/dart_to_cpp_tests.dart
diff --git a/mojo/dart/embedder/test/dart_to_cpp_tests.dart b/mojo/dart/embedder/test/dart_to_cpp_tests.dart
index 5f4af6613e2e5ed9b2bb5051c5b22d5e46ffbbdf..f71b26bdf2ddc015b786a0f629f384d8528a1538 100644
--- a/mojo/dart/embedder/test/dart_to_cpp_tests.dart
+++ b/mojo/dart/embedder/test/dart_to_cpp_tests.dart
@@ -39,14 +39,12 @@ class DartSide extends DartSideInterface {
     });
   }
 
-  void ping(params) {
+  void ping() {
     callPingResponse();
     _completer.complete(null);
   }
 
-  void echo(params) {
-    int numIterations = params.numIterations;
-    EchoArgs arg = params.arg;
+  void echo(int numIterations, EchoArgs arg) {
     if (arg.si64 > 0) {
       arg.si64 = BAD_VALUE;
     }