Stop fetching discovered printers in ArcPrintService

Currently, all printers are fetched for printing by the ArcPrintService.
Since there is no way to setup Discovered printers in ARC, let's stop
showing those printers.

Change-Id: I993fb50fc0de4bc9f87cd26fb91f837fc4a1f851
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1579423
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Auto-Submit: Bailey Berro <baileyberro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654520}

chrome/browser/chromeos/arc/print/arc_print_service.cc

@@ -15,6 +15,7 @@
 #include "base/bind_helpers.h"
 #include "base/memory/singleton.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/stl_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task/post_task.h"
 #include "chrome/browser/chrome_notification_types.h"
@@ -51,6 +52,12 @@ namespace {
 class PrintJobHostImpl;
 class PrinterDiscoverySessionHostImpl;
 
+constexpr chromeos::CupsPrintersManager::PrinterClass kClassesToFetch[] = {
+    chromeos::CupsPrintersManager::kEnterprise,
+    chromeos::CupsPrintersManager::kSaved,
+    chromeos::CupsPrintersManager::kAutomatic,
+};
+
 class ArcPrintServiceImpl : public ArcPrintService,
                             public chromeos::CupsPrintJobManager::Observer,
                             public KeyedService {
@@ -218,13 +225,14 @@ class PrinterDiscoverySessionHostImpl
   void StartPrinterDiscovery(
       const std::vector<std::string>& printer_ids) override {
     std::vector<mojom::PrinterInfoPtr> arc_printers;
-    for (size_t i = 0; i < chromeos::CupsPrintersManager::kNumPrinterClasses;
-         i++) {
-      std::vector<chromeos::Printer> printers = printers_manager_->GetPrinters(
-          static_cast<chromeos::CupsPrintersManager::PrinterClass>(i));
+
+    for (size_t i = 0; i < base::size(kClassesToFetch); ++i) {
+      auto printer_class = kClassesToFetch[i];
+      const auto& printers = printers_manager_->GetPrinters(printer_class);
       for (const auto& printer : printers)
-        arc_printers.emplace_back(ToArcPrinter(printer, nullptr));
+        arc_printers.push_back(ToArcPrinter(printer, nullptr));
     }
+
     if (!arc_printers.empty())
       instance_->AddPrinters(std::move(arc_printers));
   }