Rework service extensions to be safe

runtime/lib/developer.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.
 
 patch bool debugger({bool when: true,
                      String message}) native "Developer_debugger";
 
 patch Object inspect(Object object) native "Developer_inspect";
 
 patch void log(String message,
@@ skipping 31 matching lines @@
 int _nextSequenceNumber = 0;
 
 _log(String message,
      int timestamp,
      int sequenceNumber,
      int level,
      String name,
      Zone zone,
      Object error,
      StackTrace stackTrace) native "Developer_log";
+
+patch ServiceExtensionHandler _lookupExtension(String method)
+    native "Developer_lookupExtension";
+
+patch _registerExtension(String method, ServiceExtensionHandler handler)
+    native "Developer_registerExtension";