Simplify the ImageDataFetcher code.

components/image_fetcher/image_data_fetcher.h

 // Copyright 2016 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_IMAGE_DATA_FETCHER_H_
 #define COMPONENTS_IMAGE_FETCHER_IMAGE_DATA_FETCHER_H_
 
 #include <map>
 #include <memory>
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "net/url_request/url_fetcher_delegate.h"
 #include "url/gurl.h"
 
 namespace net {
+class URLFetcher;
 class URLRequestContextGetter;
 }  // namespace net
 
 namespace image_fetcher {
 
-class ImageDataFetcher {
+class ImageDataFetcher : public net::URLFetcherDelegate {
  public:
   using ImageDataFetcherCallback =
       base::Callback<void(const std::string& image_data)>;
 
   explicit ImageDataFetcher(
       net::URLRequestContextGetter* url_request_context_getter);
   ~ImageDataFetcher();
 
   // Fetches the raw image bytes from the given |image_url| and calls the given
   // |callback|. The callback is run even if fetching the URL fails. In case
   // of an error an empty string is passed to the callback.
   void FetchImageData(const GURL& image_url,
                       const ImageDataFetcherCallback& callback);
 
  private:
-  class ImageDataFetcherRequest;
+  struct ImageDataFetcherRequest;
 
-  // Removes the ImageDataFetcherRequest for the given |image_url| from the
-  // internal request queue.
-  void RemoveImageDataFetcherRequest(const GURL& image_url);
+  // Method inherited from URLFetcherDelegate
+  void OnURLFetchComplete(const net::URLFetcher* source) override;
 
   // All active image url requests.
-  std::map<const GURL, std::unique_ptr<ImageDataFetcherRequest>>
+  std::map<const net::URLFetcher*, std::unique_ptr<ImageDataFetcherRequest>>
       pending_requests_;
 
   scoped_refptr<net::URLRequestContextGetter> url_request_context_getter_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageDataFetcher);
 };
 
 }  // namespace image_fetcher
 
 #endif  // COMPONENTS_IMAGE_FETCHER_IMAGE_DATA_FETCHER_H_