Implement Physical Web listener registration

components/physical_web/data_source/physical_web_data_source_impl.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 COMPONENTS_PHYSICAL_WEB_DATA_SOURCE_PHYSICAL_WEB_DATA_SOURCE_IMPL_H_
+#define COMPONENTS_PHYSICAL_WEB_DATA_SOURCE_PHYSICAL_WEB_DATA_SOURCE_IMPL_H_
+
+#include "base/observer_list.h"
+#include "components/physical_web/data_source/physical_web_data_source.h"
+
+class PhysicalWebListener;
+
+class PhysicalWebDataSourceImpl : public PhysicalWebDataSource {
+ public:
+  PhysicalWebDataSourceImpl();
+  ~PhysicalWebDataSourceImpl() override;
+
+  // Register for changes to Physical Web URLs and associated page metadata.
+  void RegisterListener(PhysicalWebListener* physical_web_listener) override;
+
+  // Unregister for changes to Physical Web URLs and associated page metadata.
+  void UnregisterListener(PhysicalWebListener* physical_web_listener) override;
+
+  // Notify all registered listeners that a URL has been found.
+  void NotifyOnFound(const std::string& url);
+
+  // Notify all registered listeners that a URL has been lost.
+  void NotifyOnLost(const std::string& url);
+
+  // Notify all registered listeners that a distance has changed for a URL.
+  void NotifyOnDistanceChanged(const std::string& url,
+                               double distance_estimate);
+
+ private:
+  base::ObserverList<PhysicalWebListener> observer_list_;
+};
+
+#endif  // COMPONENTS_PHYSICAL_WEB_DATA_SOURCE_PHYSICAL_WEB_DATA_SOURCE_IMPL_H_