Upgrade to use stable `package:googleapis/v1.dart` of datastore

test/datastore/e2e/utils.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.
 
 library raw_datastore_test_utils;
 
 import 'package:gcloud/datastore.dart';
 
 const TEST_KIND = 'TestKind';
 const TEST_PROPERTY_KEY_PREFIX = 'test_property';
@@ skipping 52 matching lines @@
   return entities;
 }
 
 List<Entity> buildEntityWithAllProperties(
     int from, int to, {String kind : TEST_KIND, Partition partition}) {
   var us42 = const Duration(microseconds: 42);
   var unIndexed = new Set<String>.from(['blobProperty']);
 
   Map<String, String> buildProperties(int i) {
     return {
+      'nullValue' : null,
       'boolProperty' : true,
       'intProperty' : 42,
       'doubleProperty' : 4.2,
       'stringProperty' : 'foobar',
       'blobProperty' : new BlobValue([0xff, 0xff, 0xaa, 0xaa]),
       'blobPropertyIndexed' : new BlobValue([0xaa, 0xaa, 0xff, 0xff]),
       'dateProperty' :
           new DateTime.fromMillisecondsSinceEpoch(1, isUtc: true).add(us42),
       'keyProperty' : buildKey(1, idFunction: (i) => 's$i', kind: kind),
       'listProperty' : [
         42,
         4.2,
         'foobar',
         buildKey(1, idFunction: (i) => 's$i', kind: 'TestKind'),
       ],
     };
   }
 
   var entities = [];
   for (var i = from; i < to; i++) {
     var key = buildKey(
         i, idFunction: (i) => 'allprop$i', kind: kind, p: partition);
     var properties = buildProperties(i);
     entities.add(new Entity(key, properties, unIndexedProperties: unIndexed));
   }
   return entities;
 }