Rework service extensions to be safe

runtime/vm/json_stream.h

 // Copyright (c) 2013, 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.
 
 #ifndef VM_JSON_STREAM_H_
 #define VM_JSON_STREAM_H_
 
 #include "include/dart_api.h"  // for Dart_Port
 #include "platform/json.h"
 #include "vm/allocation.h"
@@ skipping 24 matching lines @@
 //  - runtime/vm/service/vmservice.dart
 //  - runtime/observatory/lib/src/service/object.dart
 //
 enum JSONRpcErrorCode {
   kParseError     = -32700,
   kInvalidRequest = -32600,
   kMethodNotFound = -32601,
   kInvalidParams  = -32602,
   kInternalError  = -32603,
 
+  kExtensionError = -32000,
+
   kFeatureDisabled         = 100,
   kVMMustBePaused          = 101,
   kCannotAddBreakpoint     = 102,
   kStreamAlreadySubscribed = 103,
   kStreamNotSubscribed     = 104,
 };
 
 
 class JSONStream : ValueObject {
  public:
@@ skipping 270 matching lines @@
 
   friend class JSONObject;
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(JSONArray);
 };
 
 }  // namespace dart
 
 #endif  // VM_JSON_STREAM_H_