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

ios/chrome/browser/web/external_app_launcher.mm

 // Copyright 2012 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/web/external_app_launcher.h"
 
 #include "base/ios/ios_util.h"
-#include "base/ios/weak_nsobject.h"
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/sys_string_conversions.h"
 #include "components/strings/grit/components_strings.h"
 #include "ios/chrome/browser/experimental_flags.h"
 #import "ios/chrome/browser/open_url_util.h"
 #include "ios/chrome/grit/ios_strings.h"
 #import "net/base/mac/url_conversions.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 typedef void (^AlertHandler)(UIAlertAction* action);
 
 // Returns a set of NSStrings that are URL schemes for iTunes Stores.
 NSSet<NSString*>* ITMSSchemes() {
   static NSSet<NSString*>* schemes;
   static dispatch_once_t once;
   dispatch_once(&once, ^{
     schemes =
-        [[NSSet setWithObjects:@"itms", @"itmss", @"itms-apps", @"itms-appss",
-                               // There's no evidence that itms-bookss is
-                               // actually supported, but over-inclusion
-                               // costs less than under-inclusion.
-                               @"itms-books", @"itms-bookss", nil] retain];
+        [NSSet setWithObjects:@"itms", @"itmss", @"itms-apps", @"itms-appss",
+                              // There's no evidence that itms-bookss is
+                              // actually supported, but over-inclusion
+                              // costs less than under-inclusion.
+                              @"itms-books", @"itms-bookss", nil];
   });
   return schemes;
 }
 
 bool UrlHasAppStoreScheme(const GURL& gURL) {
   std::string scheme = gURL.scheme();
   return [ITMSSchemes() containsObject:base::SysUTF8ToNSString(scheme)];
 }
 
 // Logs an entry for |Tab.ExternalApplicationOpened|.  If the user decided to
@@ skipping 139 matching lines @@
   }
 
   // If the following call returns YES, an external application is about to be
   // launched and Chrome will go into the background now.
   // TODO(crbug.com/622735): This call still needs to be updated.
   // It's heavily nested so some refactoring is needed.
   return [[UIApplication sharedApplication] openURL:URL];
 }
 
 @end