[ObjC ARC] Converts ios/chrome/app/application_delegate:application_delegate_internal to ARC.

ios/chrome/app/application_delegate/background_activity.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/app/application_delegate/background_activity.h"
 
-#import "base/ios/weak_nsobject.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/user_metrics.h"
 #include "base/metrics/user_metrics_action.h"
 #include "base/time/time.h"
 #import "ios/chrome/app/application_delegate/browser_launcher.h"
 #import "ios/chrome/app/application_delegate/metrics_mediator.h"
 #import "ios/chrome/browser/crash_report/crash_report_background_uploader.h"
 #include "ios/chrome/browser/metrics/first_user_action_recorder.h"
 #import "ios/chrome/browser/metrics/previous_session_info.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // Key of the UMA Startup.BackgroundFetchTimeInterval histogram.
 const char* const kUMAMobileBackgroundFetchTimeInterval =
     "Startup.BackgroundFetchTimeInterval";
 // Key in the UserDefaults to store the date/time that the application was last
 // launched for a background fetch.
 NSString* const kLastBackgroundFetch = @"LastBackgroundFetch";
 }  // namespace
 
 @implementation BackgroundActivity
@@ skipping 56 matching lines @@
     completionHandler();
   }
 }
 
 + (void)foregroundStarted {
   [[NSUserDefaults standardUserDefaults]
       removeObjectForKey:kLastBackgroundFetch];
 }
 
 @end