Avoid to list internal Arrays in _GetRetainingPath api

runtime/observatory/tests/service/get_retaining_path_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=--error_on_bad_type --error_on_bad_override
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 
 import 'test_helper.dart';
 
 class _TestClass {
-  _TestClass(this.x, this.y);
+  _TestClass();
   var x;
   var y;
 }
 
-var target1;
-var target2;
-var target3;
-var globalObject;
-var globalList;
+var target1 = new _TestClass();
+var target2 = new _TestClass();
+var target3 = new _TestClass();
+var globalObject = new _TestClass();
+var globalList = new List(100);
 
 void warmup() {
-  target1 = new _TestClass(null, null);
-  target2 = new _TestClass(null, null);
-  globalObject = new _TestClass(target1, target2);
-
-  target3 = new _TestClass(null, null);
-  globalList = new List(100);
+  globalObject.x = target1;
+  globalObject.y = target2;
   globalList[12] = target3;
 }
 
 eval(Isolate isolate, String expression) async {
   Map params = {
     'targetId': isolate.rootLibrary.id,
     'expression': expression,
   };
   return await isolate.invokeRpcNoUpgrade('evaluate', params);
 }
 
 var tests = [
   // simple path
   (Isolate isolate) async {
     var obj = await eval(isolate, 'globalObject');
     var params = {
       'targetId': obj['id'],
-      'limit': 4,
+      'limit': 100,
     };
     var result = await isolate.invokeRpcNoUpgrade('_getRetainingPath', params);
+    expect(result['elements'].length, equals(2));
     expect(result['elements'][1]['value']['name'], equals('globalObject'));
   },
 
   // missing limit.
   (Isolate isolate) async {
     var obj = await eval(isolate, 'globalObject');
     var params = {
       'targetId': obj['id'],
     };
     bool caughtException;
     try {
       await isolate.invokeRpcNoUpgrade('_getRetainingPath', params);
       expect(false, isTrue, reason:'Unreachable');
     } on ServerRpcException catch (e) {
       caughtException = true;
       expect(e.code, equals(ServerRpcException.kInvalidParams));
       expect(e.data['details'],
              "_getRetainingPath expects the \'limit\' parameter");
     }
     expect(caughtException, isTrue);
   },
 
   (Isolate isolate) async {
     var target1 = await eval(
         isolate, '() { var tmp = target1; target1 = null; return tmp;} ()');
     var params = {
       'targetId': target1['id'],
-      'limit': 4,
+      'limit': 100,
     };
     var result = await isolate.invokeRpcNoUpgrade('_getRetainingPath', params);
     expect(result['type'], equals('RetainingPath'));
+    print(result['elements']);
+    expect(result['elements'].length, equals(3));
     expect(result['elements'][1]['parentField']['name'], equals('x'));
     expect(result['elements'][2]['value']['name'], equals('globalObject'));
   },
 
   (Isolate isolate) async {
     var target2 = await eval(
         isolate, '() { var tmp = target2; target2 = null; return tmp;} ()');
     var params = {
       'targetId': target2['id'],
-      'limit': 4,
+      'limit': 100,
     };
     var result = await isolate.invokeRpcNoUpgrade('_getRetainingPath', params);
     expect(result['type'], equals('RetainingPath'));
+    print(result['elements']);
+    expect(result['elements'].length, equals(3));
     expect(result['elements'][1]['parentField']['name'], equals('y'));
     expect(result['elements'][2]['value']['name'], equals('globalObject'));
   },
 
   (Isolate isolate) async {
     var target3 = await eval(
         isolate, '() { var tmp = target3; target3 = null; return tmp;} ()');
     var params = {
       'targetId': target3['id'],
-      'limit': 4,
+      'limit': 100,
     };
     var result = await isolate.invokeRpcNoUpgrade('_getRetainingPath', params);
     expect(result['type'], equals('RetainingPath'));
+    print(result['elements']);
+    expect(result['elements'].length, equals(3));
     expect(result['elements'][1]['parentListIndex'], equals(12));
     expect(result['elements'][2]['value']['name'], equals('globalList'));
-  },
+  }
 ];
 
 main(args) async => runIsolateTests(args, tests, testeeBefore:warmup);