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

mojo/public/interfaces/bindings/tests/validation_test_interfaces.mojom

 // Copyright 2014 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.
 
 
 [JavaPackage="org.chromium.mojo.bindings.test.mojom.mojo"]
 module mojo.test;
 
 struct StructA {
   uint64 i;
@@ skipping 36 matching lines @@
   Method2(StructB param0, StructA param1);
   Method3(array<bool> param0);
   Method4(StructC param0, array<uint8> param1);
   Method5(StructE param0, handle<data_pipe_producer> param1);
   Method6(array<array<uint8>> param0);
   Method7(StructF param0, array<array<uint8, 3>?, 2> param1);
   Method8(array<array<string>?> param0);
   Method9(array<array<handle?>>? param0);
   Method10(map<string, uint8> param0);
   Method11(StructG param0);
+  Method12(float param0) => (float param0);
 };
 
 struct BasicStruct {
   int32 a;
 };
 
 interface IntegrationTestInterface {
   Method0(BasicStruct param0) => (array<uint8> param0);
 };