Linux: fix header includes for system protobuf.

remoting/protocol/message_decoder.h

 // Copyright (c) 2012 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 REMOTING_PROTOCOL_MESSAGE_DECODER_H_
 #define REMOTING_PROTOCOL_MESSAGE_DECODER_H_
 
 #include <deque>
 #include <list>
 
 #include "base/memory/ref_counted.h"
 #include "net/base/io_buffer.h"
 #include "remoting/base/compound_buffer.h"
+
+#if defined(USE_SYSTEM_PROTOBUF)
+#include <google/protobuf/message_lite.h>
+#else
 #include "third_party/protobuf/src/google/protobuf/message_lite.h"
+#endif
 
 namespace remoting {
 namespace protocol {
 
 // MessageDecoder uses CompoundBuffer to split the data received from
 // the network into separate messages. Each message is expected to be
 // decoded in the stream as follows:
 //   +--------------+--------------+
 //   | message_size | message_data |
 //   +--------------+--------------+
@@ skipping 27 matching lines @@
   // |next_payload_known_| is true if the size of the next payload is known.
   // After one payload is read this is reset to false.
   int next_payload_;
   bool next_payload_known_;
 };
 
 }  // namespace protocol
 }  // namespace remoting
 
 #endif  // REMOTING_PROTOCOL_MESSAGE_DECODER_H_