Polish the cleaning up url request code for parallel download.

content/browser/download/download_job.cc

Index: content/browser/download/download_job.cc
diff --git a/content/browser/download/download_job.cc b/content/browser/download/download_job.cc
index cbdf35f786da9fb037504e30ca7d8601202d0ad9..cd7f6195af9fdc673b3a7e80d6f566892d03fc2b 100644
--- a/content/browser/download/download_job.cc
+++ b/content/browser/download/download_job.cc
@@ -62,7 +62,9 @@ void DownloadJob::SetPotentialFileLength(int64_t length) {
   }
 }
 
-void DownloadJob::CancelRequestWithOffset(int64_t offset) {}
+void DownloadJob::CancelRequestWithOffset(int64_t offset) {
+  NOTREACHED();
+}
 
 bool DownloadJob::IsParallelizable() const {
   return false;