Add validation test cases for struct versioning.

mojo/public/cpp/bindings/tests/validation_unittest.cc

Index: mojo/public/cpp/bindings/tests/validation_unittest.cc
diff --git a/mojo/public/cpp/bindings/tests/validation_unittest.cc b/mojo/public/cpp/bindings/tests/validation_unittest.cc
index f8eeae3286e9c8cb0fe7749d16247a9f2635ad94..8139fe433efebde88306aab20271e0e1b1aeea50 100644
--- a/mojo/public/cpp/bindings/tests/validation_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/validation_unittest.cc
@@ -371,15 +371,6 @@ TEST_F(ValidationTest, Conformance) {
   RunValidationTests("conformance_", validators.GetHead());
 }
 
-TEST_F(ValidationTest, NotImplemented) {
-  DummyMessageReceiver dummy_receiver;
-  mojo::internal::FilterChain validators(&dummy_receiver);
-  validators.Append<mojo::internal::MessageHeaderValidator>();
-  validators.Append<ConformanceTestInterface::RequestValidator_>();
-
-  RunValidationTests("not_implemented_", validators.GetHead());
-}
-
 // Test that InterfacePtr<X> applies the correct validators and they don't
 // conflict with each other:
 //   - MessageHeaderValidator