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

ios/chrome/browser/itunes_links/itunes_links_observer.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/itunes_links/itunes_links_observer.h"
 
 #include <memory>
 
 #include "base/logging.h"
-#import "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
 #import "ios/chrome/browser/storekit_launcher.h"
 #import "ios/web/public/web_state/web_state_observer_bridge.h"
 #include "ios/web/public/web_state/web_state.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @interface ITunesLinksObserver ()
 
 // If |URL| points to a product on itunes.apple.com, returns the product ID.
 // Otherwise, returns nil.
 // Examples of URLs pointing to products on itunes.apple.com can be found in
 // itunes_links_observer_unittest.mm.
 + (NSString*)productIDFromURL:(const GURL&)URL;
 
 @end
 
 @implementation ITunesLinksObserver {
-  base::WeakNSProtocol<id<StoreKitLauncher>> _storeKitLauncher;
+  __weak id<StoreKitLauncher> _storeKitLauncher;
   std::unique_ptr<web::WebStateObserverBridge> _webStateObserverBridge;
 }
 
 - (instancetype)initWithWebState:(web::WebState*)webState {
   self = [super init];
   if (self) {
     _webStateObserverBridge.reset(
         new web::WebStateObserverBridge(webState, self));
   }
   return self;
@@ skipping 18 matching lines @@
 #pragma mark - CRWWebStateObserver
 
 - (void)webStateDidLoadPage:(web::WebState*)webState {
   GURL URL = webState->GetLastCommittedURL();
   NSString* productID = [ITunesLinksObserver productIDFromURL:URL];
   if (productID)
     [_storeKitLauncher openAppStore:productID];
 }
 
 - (void)setStoreKitLauncher:(id<StoreKitLauncher>)storeKitLauncher {
-  _storeKitLauncher.reset(storeKitLauncher);
+  _storeKitLauncher = storeKitLauncher;
 }
 
 @end