[Mojo] Add [Native] type traits for base::Values

mojo/common/test_common_custom_types.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module mojo.common.test;
 
 import "mojo/common/common_custom_types.mojom";
 
 interface TestFilePath {
   BounceFilePath(mojo.common.mojom.FilePath in)
       => (mojo.common.mojom.FilePath out);
 };
+
+interface TestValue {
+  BounceDictionaryValue(mojo.common.mojom.DictionaryValue in)
+      => (mojo.common.mojom.DictionaryValue out);
+  BounceListValue(mojo.common.mojom.ListValue in)
+      => (mojo.common.mojom.ListValue out);
+};