Add a PrinterDiscoverer fake object.

chromeos/printing/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 CHROMEOS_PRINTING_PRINTER_DISCOVERER_H_
+#define CHROMEOS_PRINTING_PRINTER_DISCOVERER_H_
+
+#include <memory>
+#include <vector>
+
+#include "chromeos/printing/printer_configuration.h"
+
+namespace chromeos {
+
+// Interface for printer discovery.  Constructs Printer objects from USB and
+// zeroconf (DNS-SD) printers.
+class PrinterDiscoverer {
+ public:
+  // Interface for objects interested in detected printers.
+  class Observer {
+   public:
+    // Called after discovery has started.
+    virtual void OnDiscoveryStarted() = 0;

[xdai1, 2016/10/03 23:34:38]

Better to not make it pure virtual? Because in the webui, I think I only need
OnPrintersFound() and OnDiscoveryDone(). 

[skau, 2016/10/03 23:52:30]

Done.

+
+    // Called when discovery is stopping.  OnPrintersFound will not be
+    // called after this occurs.
+    virtual void OnDiscoverStopping() = 0;
+
+    // Called with a collection of printers as they are discovered.  Printer
+    // objects must be copied if they are retained outside of the scope of this
+    // function.
+    virtual void OnPrintersFound(const std::vector<Printer>& printers) = 0;

[xdai1, 2016/10/03 23:34:38]

Add a "virtual void OnDiscoveryDone() {}" function to notify the observers that
the discovery is done and there is no more printers nearby (so that the spinner
on the UI page can stop)

[skau, 2016/10/03 23:52:30]

Done.

+  };
+
+  // Static factory
+  static std::unique_ptr<PrinterDiscoverer> Create();
+
+  // Begin scanning for printers.  Found printers will be reported to the
+  // attached observer.
+  virtual bool StartDiscovery() = 0;
+
+  // Stop scanning for printers.  Returns false if scanning could not be stopped
+  // and new results will continue to be be sent to observers.  Returns true if
+  // scanning was stopped successfully.  No calls to the attached observer will
+  // be made after this returns if it returned true.
+  virtual bool StopDiscovery() = 0;
+
+  // Add an observer that will be notified of discovered printers.  Ownership of
+  // |observer| is not taken by the discoverer.  It is an error to add an
+  // oberserver more than once.
+  virtual void AddObserver(PrinterDiscoverer::Observer* observer) = 0;
+
+  // Remove an observer of printer discovery.
+  virtual void RemoveObserver(PrinterDiscoverer::Observer* observer) = 0;
+};
+
+}  // namespace chromeos
+
+#endif  // CHROMEOS_PRINTING_PRINTER_DISCOVERER_H_