Add physical_web namespace

ios/chrome/browser/physical_web/create_physical_web_data_source.mm

 // 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 "ios/chrome/browser/physical_web/create_physical_web_data_source.h"
 
 #include "base/memory/ptr_util.h"
 #import "ios/chrome/browser/physical_web/ios_chrome_physical_web_data_source.h"
 
-std::unique_ptr<PhysicalWebDataSource> CreateIOSChromePhysicalWebDataSource() {
-  return base::MakeUnique<IOSChromePhysicalWebDataSource>();
+std::unique_ptr<physical_web::PhysicalWebDataSource>
+CreateIOSChromePhysicalWebDataSource() {
+  std::unique_ptr<physical_web::PhysicalWebDataSource> datasource =
+      base::MakeUnique<IOSChromePhysicalWebDataSource>();
+  return datasource;
 }