Linux: fix header includes for system protobuf.

remoting/protocol/util.h

 // Copyright (c) 2011 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.
 
 // This file defines utility methods used for encoding and decoding the protocol
 // used in Chromoting.
 
 #ifndef REMOTING_PROTOCOL_UTIL_H_
 #define REMOTING_PROTOCOL_UTIL_H_
 
 #include "net/base/io_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 {
 
 // Serialize the Protocol Buffer message and provide sufficient framing for
 // sending it over the wire.
 // This will provide sufficient prefix and suffix for the receiver side to
 // decode the message.
 scoped_refptr<net::IOBufferWithSize> SerializeAndFrameMessage(
     const google::protobuf::MessageLite& msg);
 
 }  // namespace protocol
 }  // namespace remoting
 
 #endif  // REMOTING_PROTOCOL_UTIL_H_