[ObjC ARC] Converts ios/chrome/browser/ui/elements:elements_internal to ARC.

ios/chrome/browser/ui/elements/activity_overlay_view_controller.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/ui/elements/activity_overlay_view_controller.h"
 
 #import "ios/chrome/browser/ui/material_components/activity_indicator.h"
 #import "ios/chrome/browser/ui/uikit_ui_util.h"
 #import "ios/third_party/material_components_ios/src/components/ActivityIndicator/src/MaterialActivityIndicator.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // Size of the activity indicator.
 const CGFloat kActivityIndicatorSize = 48;
 // Alpha of the presented view's background.
 const CGFloat kBackgroundAlpha = 0.5;
 }
 
 @implementation ActivityOverlayViewController
 
 - (void)viewDidLoad {
   [super viewDidLoad];
   self.view.backgroundColor = [UIColor colorWithWhite:0 alpha:kBackgroundAlpha];
 
-  MDCActivityIndicator* activityIndicator = [[[MDCActivityIndicator alloc]
+  MDCActivityIndicator* activityIndicator = [[MDCActivityIndicator alloc]
       initWithFrame:CGRectMake(0, 0, kActivityIndicatorSize,
-                               kActivityIndicatorSize)] autorelease];
+                               kActivityIndicatorSize)];
   activityIndicator.translatesAutoresizingMaskIntoConstraints = NO;
   [self.view addSubview:activityIndicator];
   AddSameCenterConstraints(self.view, activityIndicator);
   activityIndicator.cycleColors = ActivityIndicatorBrandedCycleColors();
   [activityIndicator startAnimating];
 }
 
 @end