Mojo C++ bindings: support enum validation.

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

 // Copyright 2015 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_UTIL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATION_UTIL_H_
 
 #include <stdint.h>
 
 #include "mojo/public/cpp/bindings/lib/bindings_internal.h"
@@ skipping 106 matching lines @@
 
 template <typename T>
 bool ValidateInlinedUnion(const T& input, BoundsChecker* bounds_checker) {
   return T::Validate(&input, bounds_checker, true);
 }
 
 bool ValidateHandle(const Handle& input, BoundsChecker* bounds_checker);
 
 bool ValidateAssociatedInterfaceId(InterfaceId input);
 
+// Checks whether the given enum value is valid. Please note that any value is
+// valid for an extensible enum, although it may be from a newer version and
+// thus unknown.
+template <typename T>
+bool ValidateEnum(const T& input) {
+  if (T::kIsExtensible)
+    return true;
+
+  if (T::IsKnownValue(input.value))
+    return true;
+
+  ReportValidationError(VALIDATION_ERROR_UNKNOWN_ENUM_VALUE);
+  return false;
+}
+
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATION_UTIL_H_