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

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

Index: chrome/browser/ui/webui/print_preview/print_preview_handler.cc
diff --git a/chrome/browser/ui/webui/print_preview/print_preview_handler.cc b/chrome/browser/ui/webui/print_preview/print_preview_handler.cc
index 28e220ab503a99ee2c4469da39b485b4f7a505b8..bd767fd61cd12043f240c0290a0d41ba7268828a 100644
--- a/chrome/browser/ui/webui/print_preview/print_preview_handler.cc
+++ b/chrome/browser/ui/webui/print_preview/print_preview_handler.cc
@@ -344,14 +344,22 @@ std::unique_ptr<base::DictionaryValue> GetPdfCapabilities(
   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);
@@ -360,18 +368,26 @@ std::unique_ptr<base::DictionaryValue> GetPdfCapabilities(
   }
   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() ||
@@ -410,6 +426,12 @@ std::pair<std::string, std::string> GetPrinterNameAndDescription(
 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));