Implement missing interface member in mock ModelDB

This fixes an analyzer warning

BUG=
[email protected]

Review URL: https://codereview.chromium.org//2261453002 .

Author: whesse

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.2.0+14
+
+* Fix analyzer warning.
+
 ## 0.2.0+13
 
 * Remove crypto dependency and upgrade dart dependency to >=1.13 since

pubspec.yaml

@@ -1,5 +1,5 @@
 name: gcloud
-version: 0.2.0+13
+version: 0.2.0+14
 author: Dart Team <[email protected]>
 description: Dart gcloud APIs
 homepage: https://github.com/dart-lang/gcloud

test/db/properties_test.dart

@@ -238,4 +238,5 @@ class ModelDBMock implements ModelDB {
   datastore.Entity toDatastoreEntity(Model model) => null;
   String fieldNameToPropertyName(String kind, String fieldName) => null;
   String kindName(Type type) => null;
+  Object toDatastoreValue(String kind, String fieldName, Object value) => null;
 }