Add support for JS->Dart and Dart->dart via *PortSync.

tests/html/js_interop_3_test.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file
+
+#library('JsInterop3Test');
+#import('../../lib/unittest/unittest.dart');
+#import('../../lib/unittest/html_config.dart');
+#import('dart:html');
+#import('dart:isolate');
+
+injectSource(code) {
+  final script = new ScriptElement();
+  script.type = 'text/javascript';
+  script.innerHTML = code;
+  document.body.nodes.add(script);
+}
+
+var jsToDart = """
+  var fun1 = window.lookupPort('fun1');
+  var result = fun1.callSync({'a': 'Hello', 'b': 'World', c: 42});
+
+  var fun2 = window.lookupPort('fun2');
+  fun2.callSync(result);
+""";
+
+main() {
+  useHtmlConfiguration();
+
+  test('js-to-dart', () {
+    var done = expectAsync0(() {});
+
+    var fun1 = (message) {
+      Expect.equals('Hello', message['a']);
+      Expect.equals('World', message['b']);
+      Expect.equals(42, message['c']);
+      Expect.equals(3, message.getKeys().length);
+      return 42;
+    };
+
+    var port1 = new ReceivePortSync();
+    port1.receive(fun1);
+    window.registerPort('fun1', port1.toSendPort());
+
+    var fun2 = (message) {
+      Expect.equals(42, message);
+
+      // TODO(vsm): Investigate why this needs to be called asynchronously.
+      window.setTimeout(done, 0);
+    };
+
+    var port2 = new ReceivePortSync();
+    port2.receive(fun2);
+    window.registerPort('fun2', port2.toSendPort());
+
+    injectSource(jsToDart);
+  });
+}