Move const PortName data out of header file

mojo/edk/system/ports_message.h

 // 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_H__
 #define MOJO_EDK_SYSTEM_PORTS_MESSAGE_H__
 
 #include <memory>
 #include <utility>
 
@@ skipping 42 matching lines @@
   // Construct a new PortsMessage backed by a Channel::Message. If
   // |channel_message| is null, a new one is allocated internally.
   PortsMessage(size_t num_header_bytes,
                size_t num_payload_bytes,
                size_t num_ports_bytes,
                Channel::MessagePtr channel_message);
 
   Channel::MessagePtr channel_message_;
 
   // The node name from which this message was received, if known.
-  ports::NodeName source_node_ = ports::kInvalidNodeName;
+  ports::NodeName source_node_ = ports::constants::kInvalidNodeName;
 };
 
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_PORTS_MESSAGE_H__