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

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"
 
 #include <UIKit/UIKit.h>
 
 #include "base/threading/sequenced_worker_pool.h"
 #include "components/image_fetcher/image_fetcher_delegate.h"
@@ skipping 40 matching lines @@
     return;
   }
   // Copy string reference so it's retained.
   const std::string fetch_id(id);
   ImageFetchedCallback fetcher_callback =
       ^(const GURL& original_url, int response_code, NSData* data) {
       if (data) {
         // Most likely always returns 1x images.
         UIImage* ui_image = [UIImage imageWithData:data scale:1];
         if (ui_image) {
-          gfx::Image gfx_image(ui_image);
+          gfx::Image gfx_image(ui_image, base::scoped_policy::ASSUME);
           callback.Run(fetch_id, gfx_image);
           if (delegate_) {
             delegate_->OnImageFetched(fetch_id, gfx_image);
           }
           return;
         }
       }
       gfx::Image empty_image;
       callback.Run(fetch_id, empty_image);
       if (delegate_) {
         delegate_->OnImageFetched(fetch_id, empty_image);
       }
   };
   imageFetcher_->StartDownload(image_url, fetcher_callback);
 }
 
 }  // namespace suggestions