Replace SkBitmap with gfx::Image in the ImageFetcher API.

components/image_fetcher/image_fetcher.h

 // 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.
 
 #ifndef COMPONENTS_IMAGE_FETCHER_IMAGE_FETCHER_H_
 #define COMPONENTS_IMAGE_FETCHER_IMAGE_FETCHER_H_
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "components/image_fetcher/image_fetcher_delegate.h"
 #include "url/gurl.h"
 
-class SkBitmap;
+namespace gfx {
+class Image;
+}
 
 namespace image_fetcher {
 
 // A class used to fetch server images. It can be called from any thread and the
 // callback will be called on the thread which initiated the fetch.
 class ImageFetcher {
  public:
   ImageFetcher() {}
   virtual ~ImageFetcher() {}
 
   virtual void SetImageFetcherDelegate(ImageFetcherDelegate* delegate) = 0;
 
+  // An empty gfx::Image will be returned to the callback in case the image
+  // could not be fetched.
   virtual void StartOrQueueNetworkRequest(
       const GURL& url,
       const GURL& image_url,
-      base::Callback<void(const GURL&, const SkBitmap*)> callback) = 0;
+      base::Callback<void(const GURL&, const gfx::Image&)> callback) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ImageFetcher);
 };
 
 }  // namespace image_fetcher
 
 #endif  // COMPONENTS_IMAGE_FETCHER_IMAGE_FETCHER_H_