Mojo cpp bindings: add support for validating incoming messages.

mojo/public/cpp/bindings/lib/message_header_validator.cc

Index: mojo/public/cpp/bindings/lib/message_header_validator.cc
diff --git a/mojo/public/cpp/bindings/lib/message_header_validator.cc b/mojo/public/cpp/bindings/lib/message_header_validator.cc
index a5151cfd854c9612fb701984debed877613d8fbb..1396fd1ab715dc3c685b8fe7773cf7083ebc0945 100644
--- a/mojo/public/cpp/bindings/lib/message_header_validator.cc
+++ b/mojo/public/cpp/bindings/lib/message_header_validator.cc
@@ -54,9 +54,8 @@ bool IsValidMessageHeader(const internal::MessageHeader* header) {
 
 }  // namespace
 
-MessageHeaderValidator::MessageHeaderValidator(MessageReceiver* next)
-    : next_(next) {
-  assert(next);
+MessageHeaderValidator::MessageHeaderValidator(MessageReceiver* sink)
+    : MessageFilter(sink) {
 }
 
 bool MessageHeaderValidator::Accept(Message* message) {
@@ -69,13 +68,7 @@ bool MessageHeaderValidator::Accept(Message* message) {
   if (!IsValidMessageHeader(message->header()))
     return false;
 
-  return next_->Accept(message);
-}
-
-bool MessageHeaderValidator::AcceptWithResponder(Message* message,
-                                                 MessageReceiver* responder) {
-  assert(false);  // Not reached!
-  return false;
+  return sink_->Accept(message);
 }
 
 }  // namespace internal