components/image_fetcher: Add a from_http_cache flag to RequestMetadata

components/image_fetcher/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_REQUEST_METADATA_H_
 #define COMPONENTS_IMAGE_FETCHER_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;
-  // HTTP response code.
-  int response_code;
+  int http_response_code;
+  bool from_http_cache;
 };
 
 bool operator==(const RequestMetadata& lhs, const RequestMetadata& rhs);
 bool operator!=(const RequestMetadata& lhs, const RequestMetadata& rhs);
 
 }  // namespace image_fetcher
 
 #endif  // COMPONENTS_IMAGE_FETCHER_REQUEST_METADATA_H_