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/memory/ptr_util.h"
 #include "base/threading/sequenced_worker_pool.h"
@@ skipping 43 matching lines @@
   // Copy string reference so it's retained.
   const std::string fetch_id(id);
   // If image_fetcher_ is destroyed the request will be cancelled and this block
   // will never be called. A reference to delegate_ can be kept.
   web::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);
         }
       };
   image_fetcher_->StartDownload(image_url, fetcher_callback);
 }
 
 }  // namespace suggestions