Mojo cpp bindings: add support for validating incoming messages.

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

Index: mojo/public/cpp/bindings/lib/message_header_validator.h
diff --git a/mojo/public/cpp/bindings/lib/message_header_validator.h b/mojo/public/cpp/bindings/lib/message_header_validator.h
index d7877fbf7e0ceef8a94fbfb3d550f402d761799c..5bdf47aa0845a7b069093b37b0b37148c88cb73d 100644
--- a/mojo/public/cpp/bindings/lib/message_header_validator.h
+++ b/mojo/public/cpp/bindings/lib/message_header_validator.h
@@ -2,22 +2,23 @@
 // 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_MESSAGE_HEADER_VALIDATOR_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_HEADER_VALIDATOR_H_
+
 #include "mojo/public/cpp/bindings/message.h"
+#include "mojo/public/cpp/bindings/message_filter.h"
 
 namespace mojo {
 namespace internal {
 
-class MessageHeaderValidator : public MessageReceiver {
+class MessageHeaderValidator : public MessageFilter {
  public:
-  explicit MessageHeaderValidator(MessageReceiver* next);
+  explicit MessageHeaderValidator(MessageReceiver* next = NULL);
 
   virtual bool Accept(Message* message) MOJO_OVERRIDE;
-  virtual bool AcceptWithResponder(Message* message, MessageReceiver* responder)
-      MOJO_OVERRIDE;
-
- private:
-  MessageReceiver* next_;
 };
 
 }  // namespace internal
 }  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_HEADER_VALIDATOR_H_