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

ios/chrome/browser/suggestions/image_fetcher_impl.mm

 // Copyright 2014 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/suggestions/image_fetcher_impl.h"
 
 #import <UIKit/UIKit.h>
 
 #include "base/memory/ptr_util.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "components/image_fetcher/image_fetcher_delegate.h"
 #import "ios/web/public/image_fetcher/image_data_fetcher.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "skia/ext/skia_utils_ios.h"
 #include "ui/gfx/image/image.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace suggestions {
 
 ImageFetcherImpl::ImageFetcherImpl(
     net::URLRequestContextGetter* url_request_context,
     base::SequencedWorkerPool* blocking_pool)
     : image_fetcher_(base::MakeUnique<web::ImageDataFetcher>(blocking_pool)) {
   image_fetcher_->SetRequestContextGetter(url_request_context);
 }
 
 ImageFetcherImpl::~ImageFetcherImpl() {
@@ skipping 45 matching lines @@
         gfx::Image empty_image;
         callback.Run(fetch_id, empty_image);
         if (delegate_) {
           delegate_->OnImageFetched(fetch_id, empty_image);
         }
       };
   image_fetcher_->StartDownload(image_url, fetcher_callback);
 }
 
 }  // namespace suggestions