Pass Physical Web metadata through a struct

components/physical_web/data_source/physical_web_data_source.cc

Index: components/physical_web/data_source/physical_web_data_source.cc
diff --git a/components/physical_web/data_source/physical_web_data_source.cc b/components/physical_web/data_source/physical_web_data_source.cc
index a7d9b2a2394872e3d59ef3a11e211f873cd6b0de..cd2a204f5f79a3cfc7648fe8bcbbb7ce00c371cc 100644
--- a/components/physical_web/data_source/physical_web_data_source.cc
+++ b/components/physical_web/data_source/physical_web_data_source.cc
@@ -15,4 +15,10 @@ const char kScanTimestampKey[] = "scanTimestamp";
 const char kScannedUrlKey[] = "scannedUrl";
 const char kTitleKey[] = "title";
 
+Metadata::Metadata() {}
+
+Metadata::Metadata(const Metadata& other) = default;
+
+Metadata::~Metadata() {}
+
 }  // namespace physical_web