Add a PrinterDiscoverer fake object.

chromeos/printing/printer_detector.h

Index: chromeos/printing/printer_detector.h
diff --git a/chromeos/printing/printer_detector.h b/chromeos/printing/printer_detector.h
new file mode 100644
index 0000000000000000000000000000000000000000..bb102f5db494623be7dab7affb7cb057b5bff566
--- /dev/null
+++ b/chromeos/printing/printer_detector.h
@@ -0,0 +1,51 @@
+// 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_DETECTOR_H_
+#define CHROMEOS_PRINTING_PRINTER_DETECTOR_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 PrinterDetector {
+ public:
+  // Interface for objects interested in detected printers.
+  class Observer {
+   public:
+    // Called after discovery has started.
+    virtual void OnDiscoveryStarted() = 0;
+
+    // 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.
+    virtual void OnPrintersFound(std::vector<Printer> printers) = 0;
+  };
+
+  // Static factory.  Caller is responsible for the created object.
+  static std::unique_ptr<PrinterDetector> Create();
+
+  // Begin scanning for printers.  Found printers will be reported to the
+  // attachd observer.

[xdai1, 2016/09/19 18:56:10]

nit: attached

[skau, 2016/09/20 01:56:47]

Done.

+  virtual bool StartDiscovery() = 0;
+
+  // Stop scanning for printers.  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;
+
+  // Set an observer that will be notified of discovered printers.
+  virtual void SetObserver(PrinterDetector::Observer* observer) = 0;

[xdai1, 2016/09/19 18:56:10]

How about maintaining a list of observers and then have functions like
AddObserver() and RemoveObserver()? It might benefit the use case that when the
user opens two Add printer discovery dialog in two Chrome browser windows at the
same time.

[skau, 2016/09/20 01:56:47]

Done.

+};
+
+}  // namespace chromeos
+
+#endif  // CHROMEOS_PRINTING_PRINTER_DETECTOR_H_