Add printing.dll to the component build.

printing/backend/cups_helper.h

 // Copyright (c) 2010 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 PRINTING_BACKEND_CUPS_HELPER_H_
 #define PRINTING_BACKEND_CUPS_HELPER_H_
 #pragma once
 
 #include <cups/cups.h>
 
+#include "printing/printing_export.h"
+
 class GURL;
 
 // These are helper functions for dealing with CUPS.
 namespace printing {
 
 // Helper wrapper around http_t structure, with connection and cleanup
 // functionality.
-class HttpConnectionCUPS {
+class PRINTING_EXPORT HttpConnectionCUPS {
  public:
   explicit HttpConnectionCUPS(const GURL& print_server_url);
   ~HttpConnectionCUPS();
 
   void SetBlocking(bool blocking);
 
   http_t* http();
 
  private:
   http_t* http_;
 };
 
 }  // namespace printing
 
 #endif  // PRINTING_BACKEND_CUPS_HELPER_H_