Use IOSImageDataFetcherWrapper for favicon

components/image_fetcher/image_data_fetcher.h

Index: components/image_fetcher/image_data_fetcher.h
diff --git a/components/image_fetcher/image_data_fetcher.h b/components/image_fetcher/image_data_fetcher.h
index 79f874be12cb18dd5c068cc2bd3d92a70a61585e..d05ec3d4bb55812189e7a024a0d728c0f04caae3 100644
--- a/components/image_fetcher/image_data_fetcher.h
+++ b/components/image_fetcher/image_data_fetcher.h
@@ -14,6 +14,7 @@
 #include "base/memory/ref_counted.h"
 #include "components/data_use_measurement/core/data_use_user_data.h"
 #include "components/image_fetcher/request_metadata.h"
+#include "net/url_request/url_fetcher.h"
 #include "net/url_request/url_fetcher_delegate.h"
 #include "net/url_request/url_request.h"
 #include "url/gurl.h"
@@ -27,6 +28,14 @@ namespace image_fetcher {
 
 class ImageDataFetcher : public net::URLFetcherDelegate {
  public:
+  // Impossible http response code. Used to signal that no http response code
+  // was received.
+  enum ResponseCode {
+    RESPONSE_CODE_INVALID = net::URLFetcher::RESPONSE_CODE_INVALID
+  };
+
+  // Callback with the |image_data|. If an error prevented a http response,
+  // |request_metadata.response_code| will be RESPONSE_CODE_INVALID.
   using ImageDataFetcherCallback =
       base::Callback<void(const std::string& image_data,
                           const RequestMetadata& request_metadata)>;