Mojo C++ bindings: support enum validation.

mojo/public/cpp/bindings/lib/validation_errors.h

 // 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.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATION_ERRORS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATION_ERRORS_H_
 
 #include "mojo/public/cpp/bindings/callback.h"
 #include "mojo/public/cpp/system/macros.h"
 
@@ skipping 41 matching lines @@
   VALIDATION_ERROR_MESSAGE_HEADER_INVALID_FLAGS,
   // |flags| in the message header indicates that a request ID is required but
   // there isn't one.
   VALIDATION_ERROR_MESSAGE_HEADER_MISSING_REQUEST_ID,
   // The |name| field in a message header contains an unexpected value.
   VALIDATION_ERROR_MESSAGE_HEADER_UNKNOWN_METHOD,
   // Two parallel arrays which are supposed to represent a map have different
   // lengths.
   VALIDATION_ERROR_DIFFERENT_SIZED_ARRAYS_IN_MAP,
   // Attempted to deserialize a tagged union with an unknown tag.
-  VALIDATION_ERROR_UNKNOWN_UNION_TAG
+  VALIDATION_ERROR_UNKNOWN_UNION_TAG,
+  // A value of a non-extensible enum type is unknown.
+  VALIDATION_ERROR_UNKNOWN_ENUM_VALUE
 };
 
 const char* ValidationErrorToString(ValidationError error);
 
 void ReportValidationError(ValidationError error,
                            const char* description = nullptr);
 
 // Only used by validation tests and when there is only one thread doing message
 // validation.
 class ValidationErrorObserverForTesting {
@@ skipping 49 matching lines @@
 //
 // In non-debug build, does nothing (not even compiling |condition|).
 #define MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(                        \
     condition, error, description)                                       \
   MOJO_DLOG_IF(FATAL, (condition) && !ReportSerializationWarning(error)) \
       << "The outgoing message will trigger "                            \
       << ValidationErrorToString(error) << " at the receiving side ("    \
       << description << ").";
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATION_ERRORS_H_