Mark script kinds as private in the service protocol.

runtime/observatory/tests/service/get_object_rpc_test.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.
 // VMOptions=--compile-all --error_on_bad_type --error_on_bad_override
 
 library get_object_rpc_test;
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 
@@ skipping 153 matching lines @@
     var libResult = await isolate.invokeRpcNoUpgrade('getObject', params);
     // Get the first script.
     params = {
       'objectId': libResult['scripts'][0]['id'],
     };
     var result = await isolate.invokeRpcNoUpgrade('getObject', params);
     expect(result['type'], equals('Script'));
     expect(result['id'], startsWith('libraries/'));
     expect(result['uri'], startsWith('file:'));
     expect(result['uri'], endsWith('get_object_rpc_test.dart'));
-    expect(result['kind'], equals('script'));
+    expect(result['_kind'], equals('script'));
     expect(result['library']['type'], equals('@Library'));
     expect(result['source'], startsWith('// Copyright (c)'));
     expect(result['tokenPosTable'].length, isPositive);
     expect(result['tokenPosTable'][0], new isInstanceOf<List>());
     expect(result['tokenPosTable'][0].length, isPositive);
     expect(result['tokenPosTable'][0][0], new isInstanceOf<int>());
   },
 
   // invalid script.
   (Isolate isolate) async {
@@ skipping 230 matching lines @@
       caughtException = true;
       expect(e.code, equals(ServerRpcException.kInvalidParams));
       expect(e.message,
              "getObject: invalid 'objectId' parameter: code/0");
     }
     expect(caughtException, isTrue);
   },
 ];
 
 main(args) async => runIsolateTests(args, tests, testeeBefore:warmup);