[PhysicalWeb] Add physical_web namespace.

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"
 
+namespace physical_web {
+
 PhysicalWebDataSourceImpl::PhysicalWebDataSourceImpl() {}
 
 PhysicalWebDataSourceImpl::~PhysicalWebDataSourceImpl() {}
 
 void PhysicalWebDataSourceImpl::RegisterListener(
     PhysicalWebListener* physical_web_listener) {
   observer_list_.AddObserver(physical_web_listener);
 }
 
 void PhysicalWebDataSourceImpl::UnregisterListener(
@@ skipping 10 matching lines @@
   for (PhysicalWebListener& observer : observer_list_)
     observer.OnLost(url);
 }
 
 void PhysicalWebDataSourceImpl::NotifyOnDistanceChanged(
     const std::string& url,
     double distance_estimate) {
   for (PhysicalWebListener& observer : observer_list_)
     observer.OnDistanceChanged(url, distance_estimate);
 }
+
+}  // namespace physical_web