[ObjC ARC] Converts ios/chrome/browser/physical_web:physical_web to ARC.

ios/chrome/browser/physical_web/ios_chrome_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.
 
 #import "ios/chrome/browser/physical_web/ios_chrome_physical_web_data_source.h"
 
 #include "base/memory/ptr_util.h"
 #import "ios/chrome/browser/physical_web/physical_web_initial_state_recorder.h"
 #import "ios/chrome/common/physical_web/physical_web_scanner.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 IOSChromePhysicalWebDataSource::IOSChromePhysicalWebDataSource(
     PrefService* pref_service) {
   initialStateRecorder_.reset([[PhysicalWebInitialStateRecorder alloc]
       initWithPrefService:pref_service]);
   [initialStateRecorder_ collectAndRecordState];
 }
 
 IOSChromePhysicalWebDataSource::~IOSChromePhysicalWebDataSource() {
   [initialStateRecorder_ invalidate];
   StopDiscovery();
@@ skipping 27 matching lines @@
 IOSChromePhysicalWebDataSource::GetMetadataList() {
   if (!scanner_) {
     return base::MakeUnique<physical_web::MetadataList>();
   }
   return [scanner_ metadataList];
 }
 
 bool IOSChromePhysicalWebDataSource::HasUnresolvedDiscoveries() {
   return [scanner_ unresolvedBeaconsCount] > 0;
 }