Refactor PrinterDiscoverer and PrinterDetector to use a common interface.

chrome/browser/chromeos/printing/usb_printer_detector.h

 // Copyright 2015 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_USB_PRINTER_DETECTOR_H_
 #define CHROME_BROWSER_CHROMEOS_PRINTING_USB_PRINTER_DETECTOR_H_
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
+#include "chrome/browser/chromeos/printing/printer_detector.h"
 #include "chromeos/printing/printer_configuration.h"
 #include "components/keyed_service/core/keyed_service.h"
 
 class Profile;
 
 namespace chromeos {
 
-// Observes device::UsbService for addition of USB printers (devices with
-// interface class 7).  When a device is detected, it is forwarded to the
-// printing subsystem for either autoconfiguration or user guidance.
-class UsbPrinterDetector : public KeyedService {
+// Observes device::UsbService for addition of USB printers.  When a new USB
+// printer that is not already configured for this user is found, if it can be
+// automatically configured for printing, that is done.  USB printers that
+// cannot be automatically configured are exposed via the PrinterDetector
+// interface so that higher level processing can handle them.
+class UsbPrinterDetector : public PrinterDetector, public KeyedService {
  public:
-  class Observer {
-   public:
-    virtual ~Observer() = default;
-
-    // The set of available printers has changed.
-    virtual void OnAvailableUsbPrintersChanged(
-        const std::vector<Printer>& printers) = 0;
-  };
-
   // Factory function for the CUPS implementation.
   static std::unique_ptr<UsbPrinterDetector> Create(Profile* profile);
   ~UsbPrinterDetector() override = default;
 
-  virtual void AddObserver(Observer* observer) = 0;
-  virtual void RemoveObserver(Observer* observer) = 0;
-
-  // Get the current set of detected printers.
-  virtual std::vector<Printer> GetPrinters() = 0;
-
  protected:
   UsbPrinterDetector() = default;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(UsbPrinterDetector);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_PRINTING_USB_PRINTER_DETECTOR_H_