Provide list of service protocol extensions in isolate and emit an event when one is registered

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 63 matching lines @@
         }
       });
     }
   }
 }
 
 /// A service protocol extension handler. Registered with [registerExtension].
 ///
 /// Must complete to a [ServiceExtensionResponse].
 ///
-/// [method] - the method name.
-/// [parameters] - the parameters.
+/// [method] - the method name of the service protocol request.
+/// [parameters] - A map holding the parameters to the service protocol request.
+///
+/// *NOTE*: All parameter names and values are **encoded as strings**.
 typedef Future<ServiceExtensionResponse>
-    ServiceExtensionHandler(String method, Map parameters);
+    ServiceExtensionHandler(String method, Map<String, String> parameters);
 
 /// Register a [ServiceExtensionHandler] that will be invoked in this isolate
-/// for [method].
+/// for [method]. *NOTE*: Service protocol extensions must be registered
+/// in each isolate and users of extensions must always specify a target
+/// isolate.
 void registerExtension(String method, ServiceExtensionHandler handler) {
   if (method is! String) {
     throw new ArgumentError.value(method,
                                   'method',
                                   'Must be a String');
   }
   if (_lookupExtension(method) != null) {
     throw new ArgumentError('Extension already registered: $method');
   }
   if (handler is! ServiceExtensionHandler) {
     throw new ArgumentError.value(handler,
                                   'handler',
                                   'Must be a ServiceExtensionHandler');
   }
   _registerExtension(method, handler);
 }
 
 // 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);