Fix flaky test that makes assumptions about other things on the heap

runtime/observatory/tests/service/object_graph_vm_test.dart

 // Copyright (c) 2014, 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/heap_snapshot.dart';
 import 'package:observatory/models.dart' as M;
 import 'package:observatory/object_graph.dart';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
@@ skipping 14 matching lines @@
   r = new Foo();
   var a = new Foo();
   var b = new Foo();
   r.left = a;
   r.right = b;
   a.left = b;
 
   lst = new List(2);
   lst[0] = lst; // Self-loop.
   // Larger than any other fixed-size list in a fresh heap.
-  lst[1] = new List(123456);
+  lst[1] = new List(1234569);
 }
 
 int fooId;
 
 var tests = [
   (Isolate isolate) async {
     Library lib = await isolate.rootLibrary.load();
     expect(lib.classes.length, equals(1));
     Class fooClass = lib.classes.first;
     fooId = fooClass.vmCid;
@@ skipping 43 matching lines @@
     ObjectVertex first = lists[0];
     ObjectVertex second = lists[1];
     // Check that the short list retains more than the long list inside.
     expect(first.successors.length, equals(2 + second.successors.length));
     // ... and specifically, that it retains exactly itself + the long one.
     expect(first.retainedSize, equals(first.shallowSize + second.shallowSize));
   },
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: script);