Mojo cpp bindings: add support for validating incoming messages.

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

Index: mojo/public/cpp/bindings/lib/message_filter.cc
diff --git a/mojo/public/cpp/bindings/lib/message_filter.cc b/mojo/public/cpp/bindings/lib/message_filter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b6f6b000fc4ed2aa2c3841a1b7104d9aefd275c6
--- /dev/null
+++ b/mojo/public/cpp/bindings/lib/message_filter.cc
@@ -0,0 +1,30 @@
+// Copyright 2014 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.
+
+#include "mojo/public/cpp/bindings/message_filter.h"
+
+#include <assert.h>
+
+namespace mojo {
+
+MessageFilter::MessageFilter(MessageReceiver* next) : next_(next) {
+}
+
+MessageFilter::~MessageFilter() {
+}
+
+bool MessageFilter::AcceptWithResponder(Message* message,
+                                        MessageReceiver* responder) {
+  assert(false);  // Not reached!
+  return false;
+}
+
+NullFilter::NullFilter(MessageReceiver* next) : MessageFilter(next) {
+}
+
+bool NullFilter::Accept(Message* message) {
+  return next_->Accept(message);
+}
+
+}  // namespace mojo