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

chrome/browser/ui/webui/print_preview/print_preview_handler.cc

 // Copyright (c) 2012 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 "chrome/browser/ui/webui/print_preview/print_preview_handler.h"
 
 #include <ctype.h>
 #include <stddef.h>
 
 #include <map>
@@ skipping 326 matching lines @@
       printing_context->settings().device_units_per_inch();
   return gfx::Size(pdf_media_size.width() * deviceMicronsPerDeviceUnit,
                    pdf_media_size.height() * deviceMicronsPerDeviceUnit);
 }
 
 std::unique_ptr<base::DictionaryValue> GetPdfCapabilities(
     const std::string& locale) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
   cloud_devices::CloudDeviceDescription description;
-  using namespace cloud_devices::printer;
+
+  using cloud_devices::printer::OrientationCapability;
+  using cloud_devices::printer::PORTRAIT;
+  using cloud_devices::printer::LANDSCAPE;
+  using cloud_devices::printer::AUTO_ORIENTATION;
 
   OrientationCapability orientation;
-  orientation.AddOption(cloud_devices::printer::PORTRAIT);
-  orientation.AddOption(cloud_devices::printer::LANDSCAPE);
+  orientation.AddOption(PORTRAIT);
+  orientation.AddOption(LANDSCAPE);
   orientation.AddDefaultOption(AUTO_ORIENTATION, true);
   orientation.SaveTo(&description);
 
+  using cloud_devices::printer::ColorCapability;
+  using cloud_devices::printer::Color;
+  using cloud_devices::printer::STANDARD_COLOR;
+
   ColorCapability color;
   {
     Color standard_color(STANDARD_COLOR);
     standard_color.vendor_id = base::IntToString(printing::COLOR);
     color.AddDefaultOption(standard_color, true);
   }
   color.SaveTo(&description);
 
-  static const cloud_devices::printer::MediaType kPdfMedia[] = {
-    ISO_A0,
-    ISO_A1,
-    ISO_A2,
-    ISO_A3,
-    ISO_A4,
-    ISO_A5,
-    NA_LEGAL,
-    NA_LETTER,
-    NA_LEDGER
-  };
+  using cloud_devices::printer::MediaType;
+  using cloud_devices::printer::ISO_A0;
+  using cloud_devices::printer::ISO_A1;
+  using cloud_devices::printer::ISO_A2;
+  using cloud_devices::printer::ISO_A3;
+  using cloud_devices::printer::ISO_A4;
+  using cloud_devices::printer::ISO_A5;
+  using cloud_devices::printer::NA_LEGAL;
+  using cloud_devices::printer::NA_LETTER;
+  using cloud_devices::printer::NA_LEDGER;
+
+  static const MediaType kPdfMedia[] = {ISO_A0,   ISO_A1,    ISO_A2,
+                                        ISO_A3,   ISO_A4,    ISO_A5,
+                                        NA_LEGAL, NA_LETTER, NA_LEDGER};
+
   const gfx::Size default_media_size = GetDefaultPdfMediaSizeMicrons();
+
+  using cloud_devices::printer::Media;
+  using cloud_devices::printer::MediaCapability;
+
   Media default_media(
       "", "", default_media_size.width(), default_media_size.height());
   if (!default_media.MatchBySize() ||
       std::find(kPdfMedia,
                 kPdfMedia + arraysize(kPdfMedia),
                 default_media.type) == kPdfMedia + arraysize(kPdfMedia)) {
     default_media = Media(locale == "en-US" ? NA_LETTER : ISO_A4);
   }
   MediaCapability media;
   for (size_t i = 0; i < arraysize(kPdfMedia); ++i) {
@@ skipping 18 matching lines @@
     real_description = it->second;
   return std::make_pair(real_name, real_description);
 #else
   return std::make_pair(printer.printer_name, printer.printer_description);
 #endif
 }
 
 void EnumeratePrintersOnBlockingPoolThread(base::ListValue* printers) {
   DCHECK(BrowserThread::GetBlockingPool()->RunsTasksOnCurrentThread());
 
+#if defined(OS_CHROMEOS)
+  printing::PrintBackend::SetNativeCupsEnabled(

[Lei Zhang, 2016/06/28 22:27:35]

We probably don't need to set the same value every time we enumerate printers.
How about we stick it in ChromeBrowserMainPartsLinux::PostMainMessageLoopStart()
and just call it once early on?

BTW, is the plan that |kEnableNativeCups| will eventually become always true?

[skau, 2016/06/28 23:58:19]

I've moved it to ChromeBrowserMainChromeos since this is only for Chromeos.
Yes.  The plan is to remove the flag once implementation of the backend is
complete and verified.

+      base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableNativeCups));
+#endif  // defined(OS_CHROMEOS)
+
   scoped_refptr<printing::PrintBackend> print_backend(
       printing::PrintBackend::CreateInstance(nullptr));
 
   VLOG(1) << "Enumerate printers start";
   printing::PrinterList printer_list;
   print_backend->EnumeratePrinters(&printer_list);
 
   for (const printing::PrinterBasicInfo& printer : printer_list) {
     std::unique_ptr<base::DictionaryValue> printer_info(
         new base::DictionaryValue);
@@ skipping 1371 matching lines @@
 
 void PrintPreviewHandler::UnregisterForGaiaCookieChanges() {
   if (gaia_cookie_manager_service_)
     gaia_cookie_manager_service_->RemoveObserver(this);
 }
 
 void PrintPreviewHandler::SetPdfSavedClosureForTesting(
     const base::Closure& closure) {
   pdf_file_saved_closure_ = closure;
 }