Add required CUPS include.

chrome/browser/printing/print_system_task_proxy_unittest.cc

 // 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.
 
 #include <cups/cups.h>
+#include <cups/ppd.h>
 
 #include <cstring>
 #include <string>
 #include <vector>
 
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/scoped_temp_dir.h"
 #include "chrome/browser/printing/print_system_task_proxy.h"
 #include "printing/backend/print_backend.h"
@@ skipping 267 matching lines @@
       "InvalidPrinter",
       &set_color_as_default,
       &printer_color_space_for_color,
       &printer_color_space_for_black,
       &set_duplex_as_default,
       &default_duplex_setting_value);
   ASSERT_TRUE(res);
   EXPECT_FALSE(set_duplex_as_default);
   EXPECT_EQ(printing::UNKNOWN_DUPLEX_MODE, default_duplex_setting_value);
 }