Pass Physical Web metadata through a struct

components/physical_web/data_source/physical_web_data_source.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 "components/physical_web/data_source/physical_web_data_source.h"
 
 namespace physical_web {
 
 const char kDescriptionKey[] = "description";
 const char kDistanceEstimateKey[] = "distanceEstimate";
 const char kGroupIdKey[] = "groupId";
 const char kIconUrlKey[] = "icon";
 const char kResolvedUrlKey[] = "resolvedUrl";
 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