[PhysicalWeb] Add physical_web namespace.

components/physical_web/data_source/physical_web_data_source_impl.cc

Index: components/physical_web/data_source/physical_web_data_source_impl.cc
diff --git a/components/physical_web/data_source/physical_web_data_source_impl.cc b/components/physical_web/data_source/physical_web_data_source_impl.cc
index 600a2b5e61c069949ca6e1827df3935e71ab3324..c73f2c5386111ae7fbbdda9a43fa4df1b8fe5b1e 100644
--- a/components/physical_web/data_source/physical_web_data_source_impl.cc
+++ b/components/physical_web/data_source/physical_web_data_source_impl.cc
@@ -7,6 +7,8 @@
 #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() {}
@@ -37,3 +39,5 @@ void PhysicalWebDataSourceImpl::NotifyOnDistanceChanged(
   for (PhysicalWebListener& observer : observer_list_)
     observer.OnDistanceChanged(url, distance_estimate);
 }
+
+}  // namespace physical_web