vm-service: Answer fields from superclass to subclass in declaration order (layout order).

runtime/observatory/tests/service/instance_field_order_rpc_test.dart

+// Copyright (c) 2016, 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=--error_on_bad_type --error_on_bad_override
+
+library get_object_rpc_test;
+
+import 'dart:typed_data';
+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+import 'test_helper.dart';
+
+class Super {
+  var z = 1;
+  var y = 2;
+}
+class Sub extends Super {
+  var y = 3;
+  var x = 4;
+}
+
+eval(Isolate isolate, String expression) async {
+  Map params = {
+    'targetId': isolate.rootLibrary.id,
+    'expression': expression,
+  };
+  return await isolate.invokeRpcNoUpgrade('evaluate', params);
+}
+
+var tests = [
+  (Isolate isolate) async {
+    // Call eval to get a Dart list.
+    var evalResult = await eval(isolate, 'new Sub()');
+    var params = {
+      'objectId': evalResult['id'],
+    };
+    var result = await isolate.invokeRpcNoUpgrade('getObject', params);
+    print(result);
+    expect(result['type'], equals('Instance'));
+    expect(result['kind'], equals('PlainInstance'));
+    expect(result['class']['name'], equals('Sub'));
+    expect(result['size'], isPositive);
+    expect(result['fields'][0]['decl']['name'], 'z');
+    expect(result['fields'][0]['value']['valueAsString'], '1');
+    expect(result['fields'][1]['decl']['name'], 'y');
+    expect(result['fields'][1]['value']['valueAsString'], '2');
+    expect(result['fields'][2]['decl']['name'], 'y');
+    expect(result['fields'][2]['value']['valueAsString'], '3');
+    expect(result['fields'][3]['decl']['name'], 'x');
+    expect(result['fields'][3]['value']['valueAsString'], '4');
+  },
+];
+
+main(args) async => runIsolateTests(args, tests);