Use relative URIs for core library part-of statements.

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;
+part of "developer.dart";
 
 /// A response to a service protocol extension RPC.
 ///
 /// If the RPC was successful, use [ServiceExtensionResponse.result], otherwise
 /// use [ServiceExtensionResponse.error].
 class ServiceExtensionResponse {
   final String _result;
   final int _errorCode;
   final String _errorDetail;
 
@@ skipping 148 matching lines @@
 
 external void _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);