Remove use of std::function from Mojo internals

mojo/edk/system/ports/message_filter.h

Index: mojo/edk/system/ports/message_filter.h
diff --git a/mojo/edk/system/ports/message_filter.h b/mojo/edk/system/ports/message_filter.h
new file mode 100644
index 0000000000000000000000000000000000000000..bf8fa2196659312212666dda105b85171ab5a480
--- /dev/null
+++ b/mojo/edk/system/ports/message_filter.h
@@ -0,0 +1,29 @@
+// Copyright 2016 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.
+
+#ifndef MOJO_EDK_SYSTEM_PORTS_MESSAGE_FILTER_H_
+#define MOJO_EDK_SYSTEM_PORTS_MESSAGE_FILTER_H_
+
+namespace mojo {
+namespace edk {
+namespace ports {
+
+class Message;
+
+// An interface which can be implemented to filter port messages according to
+// arbitrary policy.
+class MessageFilter {
+ public:
+  virtual ~MessageFilter() {}
+
+  // Returns true of |message| should be accepted by whomever is applying this
+  // filter. See MessageQueue::GetNextMessage(), for example.
+  virtual bool Match(const Message& message) = 0;
+};
+
+}  // namespace ports
+}  // namespace edk
+}  // namespace mojo
+
+#endif  // MOJO_EDK_SYSTEM_PORTS_MESSAGE_FILTER_H_