Add dart:developer.postEvent for posting events to the service protocol from Dart code

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=--error_on_bad_type --error_on_bad_override
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:developer';
 import 'package:observatory/service_io.dart';
 import 'package:observatory/cpu_profile.dart';
@@ skipping 38 matching lines @@
 
 Future<ServiceExtensionResponse> LanguageErrorHandler(String method,
                                                       Map paremeters) {
   // The following is an intentional syntax error.
   klajsdlkjfad
 }
 
 void test() {
   registerExtension('__delay', Handler);
   debugger();
+  postEvent('ALPHA', {
+    'cat': 'dog'
+  });
+  debugger();
   registerExtension('__error', Handler);
   registerExtension('__exception', Handler);
   registerExtension('__null', Handler);
   registerExtension('__nullFuture', Handler);
   registerExtension('__success', Handler);
   bool exceptionThrown = false;
   try {
     registerExtension('__delay', Handler);
   } catch (e) {
     exceptionThrown = true;
   }
   expect(exceptionThrown, isTrue);
   registerExtension('__languageError', LanguageErrorHandler);
 }
 
 var tests = [
   hasStoppedAtBreakpoint,
   (Isolate isolate) async {
     await isolate.load();
     expect(isolate.extensionRPCs.length, 1);
     expect(isolate.extensionRPCs[0], equals('__delay'));
   },
+  resumeIsolateAndAwaitEvent(Isolate.kExtensionStream, (ServiceEvent event) {
+    expect(event.kind, equals(ServiceEvent.kExtension));
+    expect(event.extensionKind, equals('ALPHA'));
+    expect(event.extensionData, new isInstanceOf<Map>());
+    expect(event.extensionData['cat'], equals('dog'));
+  }),
+  hasStoppedAtBreakpoint,
   resumeIsolateAndAwaitEvent(VM.kIsolateStream, (ServiceEvent event) {
     // Check that we received an event when '__error' was registered.
     expect(event.kind, equals(ServiceEvent.kServiceExtensionAdded));
     expect(event.extensionRPC, equals('__error'));
   }),
   // Initial.
   (Isolate isolate) async {
     var result;
 
     result = await isolate.invokeRpcNoUpgrade('__delay', {});
@@ skipping 45 matching lines @@
       expect(e.message, stringContainsInOrder([
           'Error in extension `__languageError`:',
           'developer_extension_test.dart',
           'semicolon expected']));
     }
 
   },
 ];
 
 main(args) async => runIsolateTests(args, tests, testeeConcurrent:test);