Add a unittest for image_data_fetcher

components/image_fetcher/image_data_fetcher.cc

 // 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.
 
 #include "components/image_fetcher/image_data_fetcher.h"
 
 #include "net/base/load_flags.h"
 #include "net/url_request/url_fetcher.h"
 #include "net/url_request/url_request.h"
 #include "net/url_request/url_request_context_getter.h"
@@ skipping 14 matching lines @@
 
   // The callback to run after the image data was fetched. The callback will
   // be run even if the image data could not be fetched successfully.
   ImageDataFetcherCallback callback;
 
   std::unique_ptr<net::URLFetcher> url_fetcher;
 };
 
 ImageDataFetcher::ImageDataFetcher(
     net::URLRequestContextGetter* url_request_context_getter)
-    : url_request_context_getter_(url_request_context_getter) {}
+    : url_request_context_getter_(url_request_context_getter),
+      next_url_fetcher_id_(0) {}
 
 ImageDataFetcher::~ImageDataFetcher() {}
 
 void ImageDataFetcher::FetchImageData(
     const GURL& url, const ImageDataFetcherCallback& callback) {
   std::unique_ptr<net::URLFetcher> url_fetcher =
-      net::URLFetcher::Create(url, net::URLFetcher::GET, this);
+      net::URLFetcher::Create(
+          next_url_fetcher_id_++, url, net::URLFetcher::GET, this);
 
   std::unique_ptr<ImageDataFetcherRequest> request(
       new ImageDataFetcherRequest(callback, std::move(url_fetcher)));
   request->url_fetcher->SetRequestContext(url_request_context_getter_.get());
   request->url_fetcher->Start();
 
   pending_requests_[request->url_fetcher.get()] = std::move(request);
 }
 
 void ImageDataFetcher::OnURLFetchComplete(const net::URLFetcher* source) {
   auto request_iter = pending_requests_.find(source);
   DCHECK(request_iter != pending_requests_.end());
 
   std::string image_data;
   if (source->GetStatus().status() == net::URLRequestStatus::SUCCESS) {
     source->GetResponseAsString(&image_data);
   }
   request_iter->second->callback.Run(image_data);
 
   // Remove the finished request.
   pending_requests_.erase(request_iter);
 }
 
 }  // namespace image_fetcher