Mojo cpp bindings: add support for validating incoming messages.

mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl

Index: mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl
index ccd4b427d8e159a2e5233c517dedcbe49916928a..4b114e7cea08e25fccf924b7b252c750ea8bb0dc 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl
@@ -236,3 +236,26 @@ bool {{class_name}}Stub::AcceptWithResponder(
 {%- endif %}
   return false;
 }
+
+{#--- Request validator definitions #}
+
+{{class_name}}RequestValidator::{{class_name}}RequestValidator(
+    mojo::MessageReceiver* next) : MessageValidator(next) {
+}
+
+bool {{class_name}}RequestValidator::Accept(mojo::Message* message) {
+  // TODO(yzshen): implement validation logic.
+  return next_->Accept(message);
+}
+
+{#--- Response validator definitions #}
+{% if interface|has_callbacks %}
+{{class_name}}ResponseValidator::{{class_name}}ResponseValidator(
+    mojo::MessageReceiver* next) : MessageValidator(next) {
+}
+
+bool {{class_name}}ResponseValidator::Accept(mojo::Message* message) {
+  // TODO(yzshen): implement validation logic.
+  return next_->Accept(message);
+}
+{%- endif -%}