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..de51eb3169a3518e3192aa23269cffc3b770560b
--- /dev/null
+++ b/chromeos/printing/printer_detector.h
@@ -0,0 +1,54 @@
+// 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;

[Carlson, 2016/10/03 18:00:51]

Should this passed vector be a const reference?

[skau, 2016/10/03 22:57:27]

yes.

+  };
+
+  // Static factory.  Caller is responsible for the created object.

[Carlson, 2016/10/03 18:00:51]

"Caller is responsible" comment is not really needed given that you're returning
a unique_ptr

[skau, 2016/10/03 22:57:27]

Done.

+  static std::unique_ptr<PrinterDetector> Create();
+
+  // Begin scanning for printers.  Found printers will be reported to the
+  // attached observer.
+  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.

[Carlson, 2016/10/03 18:00:51]

What should I expect if it returns false?

[skau, 2016/10/03 22:57:27]

Done.

+  virtual bool StopDiscovery() = 0;
+
+  // Add an observer that will be notified of discovered printers.

[Carlson, 2016/10/03 18:00:51]

Add ownership (not taken) note.

Probably also worth noting it's an error to add the same observer multiple
times.

[skau, 2016/10/03 22:57:27]

Done.

+  virtual void AddObserver(PrinterDetector::Observer* observer) = 0;
+
+  // Remove an observer of printer discovery.
+  virtual void RemoveObserver(PrinterDetector::Observer* observer) = 0;
+};
+
+}  // namespace chromeos
+
+#endif  // CHROMEOS_PRINTING_PRINTER_DETECTOR_H_