Polish the cleaning up url request code for parallel download.

content/browser/download/parallel_download_job.cc

 // 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.
 
 #include "content/browser/download/parallel_download_job.h"
 
 #include <algorithm>
 
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 82 matching lines @@
   return GetParallelRequestRemainingTimeConfig().InSeconds();
 }
 
 void ParallelDownloadJob::CancelRequestWithOffset(int64_t offset) {
   if (initial_request_offset_ == offset) {
     DownloadJobImpl::Cancel(false);
     return;
   }
 
   auto it = workers_.find(offset);
-  if (it != workers_.end())
-    it->second->Cancel();
+  DCHECK(it != workers_.end());
+  it->second->Cancel();
 }
 
 void ParallelDownloadJob::BuildParallelRequestAfterDelay() {
   DCHECK(workers_.empty());
   DCHECK(!requests_sent_);
   DCHECK(!timer_.IsRunning());
 
   timer_.Start(FROM_HERE, GetParallelRequestDelayConfig(), this,
                &ParallelDownloadJob::BuildParallelRequests);
 }
@@ skipping 128 matching lines @@
   // download request.
   download_params->set_referrer(Referrer(download_item_->GetReferrerUrl(),
                                          blink::kWebReferrerPolicyAlways));
   // Send the request.
   worker->SendRequest(std::move(download_params));
   DCHECK(workers_.find(offset) == workers_.end());
   workers_[offset] = std::move(worker);
 }
 
 }  // namespace content