Enable the cups backend when --enable-native-cups is specified.

printing/backend/print_backend_cups.h

Index: printing/backend/print_backend_cups.h
diff --git a/printing/backend/print_backend_cups.h b/printing/backend/print_backend_cups.h
new file mode 100644
index 0000000000000000000000000000000000000000..173258fdd4ff7764cbfd5fb825f9da41b47d14db
--- /dev/null
+++ b/printing/backend/print_backend_cups.h
@@ -0,0 +1,57 @@
+// Copyright 2016 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_PRINT_BACKEND_CUPS_H_
+#define PRINTING_BACKEND_PRINT_BACKEND_CUPS_H_
+
+#include <string>
+
+#include "base/files/file_util.h"
+#include "printing/backend/cups_helper.h"
+#include "printing/backend/print_backend.h"
+#include "url/gurl.h"
+
+namespace printing {
+
+class PrintBackendCUPS : public PrintBackend {
+ public:
+  PrintBackendCUPS(const GURL& print_server_url,
+                   http_encryption_t encryption,
+                   bool blocking);
+
+ private:
+  ~PrintBackendCUPS() override {}
+
+  // PrintBackend implementation.
+  bool EnumeratePrinters(PrinterList* printer_list) override;
+  std::string GetDefaultPrinterName() override;
+  bool GetPrinterBasicInfo(const std::string& printer_name,
+                           PrinterBasicInfo* printer_info) override;
+  bool GetPrinterSemanticCapsAndDefaults(
+      const std::string& printer_name,
+      PrinterSemanticCapsAndDefaults* printer_info) override;
+  bool GetPrinterCapsAndDefaults(const std::string& printer_name,
+                                 PrinterCapsAndDefaults* printer_info) override;
+  std::string GetPrinterDriverInfo(const std::string& printer_name) override;
+  bool IsValidPrinter(const std::string& printer_name) override;
+
+  // The following functions are wrappers around corresponding CUPS functions.
+  // <functions>2() are called when print server is specified, and plain version
+  // in another case. There is an issue specifying CUPS_HTTP_DEFAULT in the
+  // functions>2(), it does not work in CUPS prior to 1.4.
+  int GetDests(cups_dest_t** dests);
+  base::FilePath GetPPD(const char* name);
+
+  // Wrapper around cupsGetNamedDest(). Returned result should be freed with
+  // cupsFreeDests().
+  cups_dest_t* GetNamedDest(const std::string& printer_name);
+
+  GURL print_server_url_;
+  http_encryption_t cups_encryption_;
+  bool blocking_;
+};
+
+}  // namespace printing
+
+#endif  // PRINTING_BACKEND_PRINT_BACKEND_CUPS_H_