Implement Physical Web listener registration

components/physical_web/data_source/physical_web_data_source_impl.cc

+// 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.
+
+#include "base/observer_list.h"
+#include "components/physical_web/data_source/physical_web_data_source.h"
+#include "components/physical_web/data_source/physical_web_data_source_impl.h"
+#include "components/physical_web/data_source/physical_web_listener.h"
+
+PhysicalWebDataSourceImpl::PhysicalWebDataSourceImpl() {}
+
+PhysicalWebDataSourceImpl::~PhysicalWebDataSourceImpl() {}
+
+void PhysicalWebDataSourceImpl::RegisterListener(
+    PhysicalWebListener* physical_web_listener) {
+  observer_list_.AddObserver(physical_web_listener);
+}
+
+void PhysicalWebDataSourceImpl::UnregisterListener(
+    PhysicalWebListener* physical_web_listener) {
+  observer_list_.RemoveObserver(physical_web_listener);
+}
+
+void PhysicalWebDataSourceImpl::NotifyOnFound(const std::string& url) {
+  FOR_EACH_OBSERVER(PhysicalWebListener, observer_list_, OnFound(url));
+}
+
+void PhysicalWebDataSourceImpl::NotifyOnLost(const std::string& url) {
+  FOR_EACH_OBSERVER(PhysicalWebListener, observer_list_, OnLost(url));
+}
+
+void PhysicalWebDataSourceImpl::NotifyOnDistanceChanged(
+    const std::string& url,
+    double distance_estimate) {
+  FOR_EACH_OBSERVER(PhysicalWebListener, observer_list_,
+                    OnDistanceChanged(url, distance_estimate));
+}