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

ios/chrome/browser/physical_web/start_physical_web_discovery.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/start_physical_web_discovery.h"
 
 #import <CoreLocation/CoreLocation.h>
 
 #include "components/physical_web/data_source/physical_web_data_source.h"
 #include "components/search_engines/search_terms_data.h"
 #include "components/search_engines/template_url_service.h"
 #include "ios/chrome/browser/application_context.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #import "ios/chrome/browser/experimental_flags.h"
 #import "ios/chrome/browser/geolocation/omnibox_geolocation_config.h"
 #include "ios/chrome/browser/physical_web/physical_web_constants.h"
 #include "ios/chrome/browser/pref_names.h"
 #include "ios/chrome/browser/search_engines/template_url_service_factory.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 void StartPhysicalWebDiscovery(PrefService* pref_service,
                                ios::ChromeBrowserState* browser_state) {
   // Do not scan if the Physical Web feature is disabled by a command line flag
   // or Chrome Variations experiment.
   if (!experimental_flags::IsPhysicalWebEnabled()) {
     return;
   }
 
   // If the preference is in the default state, check if conditions allow us to
   // auto-enable it. The preference can be auto-enabled if the omnibox would
@@ skipping 37 matching lines @@
   }
 
   // Scan only if the feature is enabled.
   if (preference_state == physical_web::kPhysicalWebOn) {
     GetApplicationContext()->GetPhysicalWebDataSource()->StartDiscovery(true);
   } else {
     GetApplicationContext()->GetPhysicalWebDataSource()->StopDiscovery();
   }
 }