[NTP Snippets] Cache images in a LevelDB

components/image_fetcher/image_fetcher_delegate.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_DELEGATE_H_
 #define COMPONENTS_IMAGE_FETCHER_IMAGE_FETCHER_DELEGATE_H_
 
+#include <string>
+
 #include "base/macros.h"
 
-class GURL;
-
 namespace gfx {
 class Image;
 }
 
 namespace image_fetcher {
 
 class ImageFetcherDelegate {
  public:
   ImageFetcherDelegate() {}
 
-  // Called when an image was fetched. |id| is an identifier for the fetch (as
-  // passed to ImageFetcher::StartOrQueueNetworkRequest); |image| stores image
-  // data owned by the caller, and can be an empty gfx::Image.
+  // Called when the data for an image was fetched. |id| is an identifier for
+  // the fetch (as passed to ImageFetcher::StartOrQueueNetworkRequest); |data|
+  // stores (generally compressed) image data owned by the caller, and can be
+  // empty if the fetch failed.
+  virtual void OnImageDataFetched(const std::string& id,
+                                  const std::string& data) {};
+
+  // Called when an image was fetched and decoded. |id| is an identifier for the
+  // fetch (as passed to ImageFetcher::StartOrQueueNetworkRequest); |image|
+  // stores image data owned by the caller, and can be an empty gfx::Image.
   virtual void OnImageFetched(const std::string& id,
-                              const gfx::Image& image) = 0;
+                              const gfx::Image& image) {};
 
  protected:
   virtual ~ImageFetcherDelegate() {}
 
   DISALLOW_COPY_AND_ASSIGN(ImageFetcherDelegate);
 };
 
 }  // namespace image_fetcher
 
 #endif  // COMPONENTS_IMAGE_FETCHER_IMAGE_FETCHER_DELEGATE_H_