[NTP Snippets] Cache images in a LevelDB

components/image_fetcher/image_fetcher_delegate.h

Index: components/image_fetcher/image_fetcher_delegate.h
diff --git a/components/image_fetcher/image_fetcher_delegate.h b/components/image_fetcher/image_fetcher_delegate.h
index dc5b83fbea9a2c90beed04bf02b2c745785abf31..38d66b29543987477deaa42660f306e40d538aa4 100644
--- a/components/image_fetcher/image_fetcher_delegate.h
+++ b/components/image_fetcher/image_fetcher_delegate.h
@@ -5,9 +5,9 @@
 #ifndef COMPONENTS_IMAGE_FETCHER_IMAGE_FETCHER_DELEGATE_H_
 #define COMPONENTS_IMAGE_FETCHER_IMAGE_FETCHER_DELEGATE_H_
 
-#include "base/macros.h"
+#include <string>
 
-class GURL;
+#include "base/macros.h"
 
 namespace gfx {
 class Image;
@@ -19,11 +19,18 @@ 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() {}