Make CUPS USB printing play better with the settings page. This change does several things:

chrome/browser/chromeos/printing/fake_printer_discoverer.h

-// 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 CHROME_BROWSER_CHROMEOS_PRINTING_FAKE_PRINTER_DISCOVERER_H_
-#define CHROME_BROWSER_CHROMEOS_PRINTING_FAKE_PRINTER_DISCOVERER_H_
-
-#include <vector>
-
-#include "base/macros.h"
-#include "base/memory/weak_ptr.h"
-#include "chrome/browser/chromeos/printing/printer_discoverer.h"
-#include "chromeos/printing/printer_configuration.h"
-
-namespace chromeos {
-
-class FakePrinterDiscoverer : public PrinterDiscoverer {
- public:
-  FakePrinterDiscoverer();
-  ~FakePrinterDiscoverer() override;
-
-  bool StartDiscovery() override;
-  bool StopDiscovery() override;
-  void AddObserver(PrinterDiscoverer::Observer* observer) override;
-  void RemoveObserver(PrinterDiscoverer::Observer* observer) override;
-
- private:
-  void EmitPrinters(size_t start, size_t end);
-
-  std::vector<chromeos::Printer> printers_;
-  bool discovery_running_;
-  std::vector<PrinterDiscoverer::Observer*> observers_;
-
-  base::WeakPtrFactory<FakePrinterDiscoverer> weak_ptr_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(FakePrinterDiscoverer);
-};
-
-}  // namespace chromeos
-
-#endif  // CHROME_BROWSER_CHROMEOS_PRINTING_FAKE_PRINTER_DISCOVERER_H_