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

ios/chrome/browser/itunes_links/itunes_links_observer.mm

Index: ios/chrome/browser/itunes_links/itunes_links_observer.mm
diff --git a/ios/chrome/browser/itunes_links/itunes_links_observer.mm b/ios/chrome/browser/itunes_links/itunes_links_observer.mm
index c881fd6930dd9eb350921ed4479a38e23d2564a8..3ba6a3546d6b70bae6bb3566f0cd716ced092cfc 100644
--- a/ios/chrome/browser/itunes_links/itunes_links_observer.mm
+++ b/ios/chrome/browser/itunes_links/itunes_links_observer.mm
@@ -7,13 +7,16 @@
 #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.
@@ -25,7 +28,7 @@
 @end
 
 @implementation ITunesLinksObserver {
-  base::WeakNSProtocol<id<StoreKitLauncher>> _storeKitLauncher;
+  __weak id<StoreKitLauncher> _storeKitLauncher;
   std::unique_ptr<web::WebStateObserverBridge> _webStateObserverBridge;
 }
 
@@ -64,7 +67,7 @@
 }
 
 - (void)setStoreKitLauncher:(id<StoreKitLauncher>)storeKitLauncher {
-  _storeKitLauncher.reset(storeKitLauncher);
+  _storeKitLauncher = storeKitLauncher;
 }
 
 @end