[ImageFetcher] Return http response headers

components/image_fetcher/core/request_metadata.h

 // Copyright 2017 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_CORE_REQUEST_METADATA_H_
 #define COMPONENTS_IMAGE_FETCHER_CORE_REQUEST_METADATA_H_
 
 #include <string>
 
 #include "net/url_request/url_fetcher.h"
 
 namespace image_fetcher {
 
 // Metadata for a URL request.
 struct RequestMetadata {
   // Impossible http response code. Used to signal that no http response code
   // was received.
   enum ResponseCode {
     RESPONSE_CODE_INVALID = net::URLFetcher::RESPONSE_CODE_INVALID
   };
 
   RequestMetadata();
 
   std::string mime_type;
   int http_response_code;
   bool from_http_cache;
+
+  // Is guaranteed to be a valid pointer only when the callback is called. The
+  // headers may get deleted right after the callback finishes.
+  // TODO(jkrcal): Remove |mime_type| and |http_response_code| as it all can be
+  // read from HttpResponseHeaders.
+  net::HttpResponseHeaders* http_response_headers;
 };
 
 bool operator==(const RequestMetadata& lhs, const RequestMetadata& rhs);
 bool operator!=(const RequestMetadata& lhs, const RequestMetadata& rhs);
 
 }  // namespace image_fetcher
 
 #endif  // COMPONENTS_IMAGE_FETCHER_CORE_REQUEST_METADATA_H_