Refactor PrinterDiscoverer and PrinterDetector to use a common interface.

chrome/browser/chromeos/printing/printer_detector.h

+// Copyright 2017 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_PRINTER_DETECTOR_H_
+#define CHROME_BROWSER_CHROMEOS_PRINTING_PRINTER_DETECTOR_H_
+
+#include <vector>
+
+#include "chromeos/printing/printer_configuration.h"
+
+namespace chromeos {
+
+// Interface for automatic printer detection.  This API allows for
+// incremental discovery of printers and notification when discovery
+// is complete.
+//
+// All of the interface calls in this class must be called from the
+// same sequence, but do not have to be on any specific thread.
+//
+// The usual usage of this interface by a class that wants to maintain
+// an up-to-date list of the printers detected is this:
+//
+// auto detector_ = PrinterDetectorImplementation::Create();
+// detector_->AddObserver(this);
+// printers_ = detector_->GetPrinters();
+//
+class CHROMEOS_EXPORT PrinterDetector {
+ public:
+  class Observer {
+   public:
+    virtual ~Observer() = default;
+
+    // Called with a collection of printers as they are discovered.  On each
+    // call |printers| is the full set of known printers; it is not
+    // incremental; printers may be added or removed.
+    virtual void OnPrintersFound(const std::vector<Printer>& printers) = 0;
+
+    // Called when we are done with the initial scan for printers.  We may
+    // still call OnPrintersFound if the set of available printers
+    // changes, but the user can conclude that if a printer is currently
+    // available and not in the list, we're not still looking for it.
+    virtual void OnPrinterScanComplete() = 0;
+  };
+
+  virtual ~PrinterDetector() = default;
+
+  // Start scanning for printers.  No observer callbacks will be performed
+  // until this is called.
+  virtual void Start() = 0;
+
+  // Observer management.  Observer callbacks will be performed on the
+  // calling sequence.
+  virtual void AddObserver(Observer* observer) = 0;
+  virtual void RemoveObserver(Observer* observer) = 0;
+
+  // Get the current list of known printers.
+  virtual std::vector<Printer> GetPrinters() = 0;
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_PRINTING_PRINTER_DETECTOR_H_