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

ios/chrome/browser/ui/background_generator.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.
 
 #include "ios/chrome/browser/ui/background_generator.h"
 
 #import <QuartzCore/QuartzCore.h>
 #include <stddef.h>
 
 #include "base/mac/bundle_locations.h"
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_cftyperef.h"
-#import "base/mac/scoped_nsobject.h"
 #import "ios/chrome/browser/ui/ui_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 // This is a utility function that may be used as a standalone helper function
 // to generate a radial gradient UIImage.
 UIImage* GetRadialGradient(CGRect backgroundRect,
                            CGPoint centerPoint,
                            CGFloat radius,
                            CGFloat centerColor,
                            CGFloat outsideColor,
                            UIImage* tileImage,
                            UIImage* logoImage) {
   UIGraphicsBeginImageContextWithOptions(backgroundRect.size, YES, 0);
@@ skipping 15 matching lines @@
         CGPointMake(centerPoint.x - logoImage.size.width / 2.0,
                     centerPoint.y - logoImage.size.height / 2.0));
     [logoImage drawAtPoint:corner];
   }
   UIImage* background = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();
   return background;
 }
 
 void InstallBackgroundInView(UIView* view) {
-  UIImageView* imageView =
-      [[[UIImageView alloc] initWithFrame:view.bounds] autorelease];
+  UIImageView* imageView = [[UIImageView alloc] initWithFrame:view.bounds];
   imageView.image = [UIImage imageNamed:@"stack_view_background_noise.jpg"];
   imageView.contentMode = UIViewContentModeScaleAspectFill;
   imageView.autoresizingMask =
       UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
   [view insertSubview:imageView atIndex:0];
 }