Add printing.dll to the component build.

printing/backend/cups_helper.h

Index: printing/backend/cups_helper.h
===================================================================
--- printing/backend/cups_helper.h	(revision 99019)
+++ printing/backend/cups_helper.h	(working copy)
@@ -8,6 +8,8 @@
 
 #include <cups/cups.h>
 
+#include "printing/printing_export.h"
+
 class GURL;
 
 // These are helper functions for dealing with CUPS.
@@ -15,7 +17,7 @@
 
 // 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();