Cpp bindings: Return false from Validator::Accept() on unrecognized message or invalid flags

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 8139fe433efebde88306aab20271e0e1b1aeea50..750a54e5e11fac81487d9eaa991e666d2a412a56 100644
--- a/mojo/public/cpp/bindings/tests/validation_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/validation_unittest.cc
@@ -371,6 +371,16 @@ TEST_F(ValidationTest, Conformance) {
   RunValidationTests("conformance_", validators.GetHead());
 }
 
+// This test is similar to the Conformance test but for responses.
+TEST_F(ValidationTest, Response) {
+  DummyMessageReceiver dummy_receiver;
+  mojo::internal::FilterChain validators(&dummy_receiver);
+  validators.Append<mojo::internal::MessageHeaderValidator>();
+  validators.Append<ConformanceTestInterface::ResponseValidator_>();
+
+  RunValidationTests("response_", validators.GetHead());
+}
+
 // Test that InterfacePtr<X> applies the correct validators and they don't
 // conflict with each other:
 //   - MessageHeaderValidator