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

components/image_fetcher/image_fetcher.h

Index: components/image_fetcher/image_fetcher.h
diff --git a/components/image_fetcher/image_fetcher.h b/components/image_fetcher/image_fetcher.h
index 04f417c66b68af0e11dbfb30a3ede7993d3dd50a..b5219ba66dfde966d882d4f95eab589c43cead98 100644
--- a/components/image_fetcher/image_fetcher.h
+++ b/components/image_fetcher/image_fetcher.h
@@ -10,12 +10,16 @@
 #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.
+// callback will be called on the thread which initiated the fetch. An empty
+// gfx::Image will be returned to the callback in case the image could not be
+// fetched.
 class ImageFetcher {
  public:
   ImageFetcher() {}
@@ -26,7 +30,7 @@ class ImageFetcher {
   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);