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

sdk/lib/developer/extension.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.
 
 part of dart.developer;
 
 class ServiceExtensionResponse {
   final String _result;
   final int _errorCode;
   final String _errorDetail;
@@ skipping 91 matching lines @@
     throw new ArgumentError('Extension already registered: $method');
   }
   if (handler is! ServiceExtensionHandler) {
     throw new ArgumentError.value(handler,
                                   'handler',
                                   'Must be a ServiceExtensionHandler');
   }
   _registerExtension(method, handler);
 }
 
+/// Post an event of [eventKind] with payload of [eventData] to the `Extension`
+/// event stream.
+void postEvent(String eventKind, Map eventData) {
+  if (eventKind is! String) {
+    throw new ArgumentError.value(eventKind,
+                                  'eventKind',
+                                  'Must be a String');
+  }
+  if (eventData is! Map) {
+    throw new ArgumentError.value(eventData,
+                                  'eventData',
+                                  'Must be a Map');
+  }
+  String eventDataAsString = JSON.encode(eventData);
+  _postEvent(eventKind, eventDataAsString);
+}
+
+external _postEvent(String eventKind, String eventData);
+
 // Both of these functions are written inside C++ to avoid updating the data
 // structures in Dart, getting an OOB, and observing stale state. Do not move
 // these into Dart code unless you can ensure that the operations will can be
 // done atomically. Native code lives in vm/isolate.cc-
 // LookupServiceExtensionHandler and RegisterServiceExtensionHandler.
 external ServiceExtensionHandler _lookupExtension(String method);
 external _registerExtension(String method, ServiceExtensionHandler handler);