Enable DNS-SD discovery for cast devices (see issue #2900)

BUILD.gn

@@ -253,7 +253,6 @@ if (is_linux) {
 # Set ENABLE_PRINTING=1 ENABLE_BASIC_PRINTING=1.
 assert(enable_basic_printing)
 assert(enable_print_preview)
-assert(!enable_service_discovery)
 
 # Enable support for Widevine CDM.
 assert(enable_widevine)

patch/patches/print_preview_123.patch

@@ -262,7 +262,7 @@ index 0881b3dd9303..4df6883d4d05 100644
    Profile* const profile_;
    PrintPreviewStickySettings* const sticky_settings_;
 diff --git chrome/browser/ui/webui/print_preview/print_preview_handler.cc chrome/browser/ui/webui/print_preview/print_preview_handler.cc
-index 113d34201f90..8834b94c5475 100644
+index 113d34201f90..4a75044c2bb7 100644
 --- chrome/browser/ui/webui/print_preview/print_preview_handler.cc
 +++ chrome/browser/ui/webui/print_preview/print_preview_handler.cc
 @@ -27,6 +27,7 @@
@@ -282,6 +282,15 @@ index 113d34201f90..8834b94c5475 100644
      initial_settings.SetStringKey(
          kCloudPrintURL, GURL(cloud_devices::GetCloudPrintURL()).spec());
    }
+@@ -1403,7 +1404,7 @@ PrinterHandler* PrintPreviewHandler::GetPrinterHandler(
+     }
+     return extension_printer_handler_.get();
+   }
+-#if BUILDFLAG(ENABLE_SERVICE_DISCOVERY)
++#if BUILDFLAG(ENABLE_SERVICE_DISCOVERY) && !BUILDFLAG(ENABLE_CEF)
+   if (printer_type == PrinterType::kPrivetPrinter) {
+     if (!privet_printer_handler_) {
+       privet_printer_handler_ =
 @@ -1411,6 +1412,9 @@ PrinterHandler* PrintPreviewHandler::GetPrinterHandler(
      }
      return privet_printer_handler_.get();

tools/gn_args.py

@@ -246,7 +246,6 @@ def GetRequiredArgs():
       # ENABLE_SERVICE_DISCOVERY=0 for print preview support
       'enable_print_preview': True,
       'optimize_webui': True,
-      'enable_service_discovery': False,
       # Enable support for Widevine CDM.
       'enable_widevine': True,