Mojo cpp bindings: report the reason of validation failure.

mojo/public/tools/bindings/generators/cpp_templates/module.cc.tmpl

 // Copyright 2013 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.
 
 #if defined(__clang__)
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wunused-private-field"
 #endif
 
 #include "{{module.path}}.h"
 
 #include "mojo/public/cpp/bindings/lib/array_serialization.h"
 #include "mojo/public/cpp/bindings/lib/bindings_serialization.h"
 #include "mojo/public/cpp/bindings/lib/bounds_checker.h"
 #include "mojo/public/cpp/bindings/lib/message_builder.h"
 #include "mojo/public/cpp/bindings/lib/string_serialization.h"
+#include "mojo/public/cpp/bindings/lib/validation_errors.h"
 
 {%- for namespace in namespaces_as_array %}
 namespace {{namespace}} {
 {%- endfor %}
 
 {#--- Constants #}
 {%  for constant in module.constants %}
 const {{constant.kind|cpp_pod_type}} {{constant.name}} = {{constant.value|expression_to_text(module)}};
 {%- endfor %}
 
@@ skipping 49 matching lines @@
 {%-   include "struct_serialization_definition.tmpl" %}
 {%- endfor %}
 
 {%- for namespace in namespaces_as_array|reverse %}
 }  // namespace {{namespace}}
 {%- endfor %}
 
 #if defined(__clang__)
 #pragma clang diagnostic pop
 #endif