Add physical_web namespace

ios/chrome/browser/physical_web/create_physical_web_data_source.h

Index: ios/chrome/browser/physical_web/create_physical_web_data_source.h
diff --git a/ios/chrome/browser/physical_web/create_physical_web_data_source.h b/ios/chrome/browser/physical_web/create_physical_web_data_source.h
index 098a853a54e7301a8073a91e08221f16c58d9058..7ecddef6b8e7e6d1bab200b48ed66b56300b25a0 100644
--- a/ios/chrome/browser/physical_web/create_physical_web_data_source.h
+++ b/ios/chrome/browser/physical_web/create_physical_web_data_source.h
@@ -7,10 +7,13 @@
 
 #include <memory>
 
+namespace physical_web {
 class PhysicalWebDataSource;
+}
 
 // Creates a new instance of IOSChromePhysicalWebDataSource. The returned object
 // is fully initialized and can be registered as global singleton.
-std::unique_ptr<PhysicalWebDataSource> CreateIOSChromePhysicalWebDataSource();
+std::unique_ptr<physical_web::PhysicalWebDataSource>
+CreateIOSChromePhysicalWebDataSource();
 
 #endif  // IOS_CHROME_BROWSER_PHYSICAL_WEB_CREATE_PHYSICAL_WEB_DATA_SOURCE_H_