Allow Dart code to register service protocol handlers

runtime/observatory/tests/service/developer_extension_test.dart

+// Copyright (c) 2015, 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.
+// VMOptions=--compile_all --error_on_bad_type --error_on_bad_override
+
+import 'dart:convert';
+import 'dart:developer';
+import 'package:observatory/service_io.dart';
+import 'package:observatory/cpu_profile.dart';
+import 'package:unittest/unittest.dart';
+
+import 'test_helper.dart';
+
+void Handler(String method,
+             Map paremeters,
+             List<String> response) {
+  assert(response.length == 3);
+  if (method == '__success') {
+    response[kResultIndex] = JSON.encode({
+      'type': '_extensionType',
+      'method': method,
+      'parameters': paremeters,
+    });
+  } else {
+    response[kErrorCodeIndex] = 99;
+    response[kErrorMessageIndex] = 'extension error';
+  }
+}
+
+void test() {
+  registerExtension('__error', Handler);
+  registerExtension('__success', Handler);
+}
+
+var tests = [
+  // Initial.
+  (Isolate isolate) async {
+    try {
+      await isolate.invokeRpcNoUpgrade('__error', {});
+    } on ServerRpcException catch (e, st) {
+      expect(e.code, equals(99));
+      expect(e.message, equals("extension error"));
+    }
+    var result = await isolate.invokeRpcNoUpgrade('__success',
+                                                  {'apple': 'banana'});
+    expect(result['type'], equals('_extensionType'));
+    expect(result['method'], equals('__success'));
+    expect(result['parameters']['isolateId'], isNotNull);
+    expect(result['parameters']['apple'], equals('banana'));
+  },
+];
+
+main(args) async => runIsolateTests(args, tests, testeeBefore:test);