Adds a new constructor for gfx::Image on iOS.

ios/chrome/browser/suggestions/ios_image_decoder_impl.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.
 
 #include "ios/chrome/browser/suggestions/ios_image_decoder_impl.h"
 
 #include <UIKit/UIKit.h>
 
 #include "base/callback.h"
 #include "base/mac/scoped_nsobject.h"
@@ skipping 130 matching lines @@
     const image_fetcher::ImageDecodedCallback& callback,
     const base::scoped_nsobject<NSData>& image_data) {
   // Decode the image data using UIImage.
   if (image_data) {
     // "Most likely" always returns 1x images.
     UIImage* ui_image = [UIImage imageWithData:image_data scale:1];
     if (ui_image) {
       // This constructor does not retain the image, but expects to take the
       // ownership, therefore, |ui_image| is retained here, but not released
       // afterwards.
-      gfx::Image gfx_image([ui_image retain]);
+      gfx::Image gfx_image(ui_image, base::scoped_policy::RETAIN);
       callback.Run(gfx_image);
       return;
     }
   }
   gfx::Image empty_image;
   callback.Run(empty_image);
 }
 
 std::unique_ptr<image_fetcher::ImageDecoder> CreateIOSImageDecoder(
     scoped_refptr<base::TaskRunner> task_runner) {
   return base::MakeUnique<IOSImageDecoderImpl>(std::move(task_runner));
 }
 
 }  // namespace suggestions