[ObjC ARC] Converts components/history/ios/browser:browser to ARC.

components/history/ios/browser/web_state_top_sites_observer.mm

 // Copyright 2015 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/history/ios/browser/web_state_top_sites_observer.h"
 
 #include "base/logging.h"
 #include "components/history/core/browser/top_sites.h"
 #include "ios/web/public/load_committed_details.h"
 #include "ios/web/public/navigation_item.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 DEFINE_WEB_STATE_USER_DATA_KEY(history::WebStateTopSitesObserver);
 
 namespace history {
 
 // static
 void WebStateTopSitesObserver::CreateForWebState(web::WebState* web_state,
                                                  TopSites* top_sites) {
   DCHECK(web_state);
   if (!FromWebState(web_state)) {
     web_state->SetUserData(UserDataKey(),
@@ skipping 10 matching lines @@
 }
 
 void WebStateTopSitesObserver::NavigationItemCommitted(
     const web::LoadCommittedDetails& load_details) {
   DCHECK(load_details.item);
   if (top_sites_)
     top_sites_->OnNavigationCommitted(load_details.item->GetURL());
 }
 
 }  // namespace history