Add UMA for estimating disk bandwidth and the time saved with parallel download

content/browser/download/download_file_impl.h

Index: content/browser/download/download_file_impl.h
diff --git a/content/browser/download/download_file_impl.h b/content/browser/download/download_file_impl.h
index 61f1f4d90bb054a524b32e402f78111c7d1de5a0..da7a66e880012b6ddca3fd2b8d63a44d3f12eaf7 100644
--- a/content/browser/download/download_file_impl.h
+++ b/content/browser/download/download_file_impl.h
@@ -223,6 +223,11 @@ class CONTENT_EXPORT DownloadFileImpl : public DownloadFile {
   base::TimeDelta disk_writes_time_;
   base::TimeTicks download_start_;
   RateEstimator rate_estimator_;
+  int num_active_streams_;
+  size_t bytes_seen_with_parallel_streams_;
+  size_t bytes_seen_without_parallel_streams_;
+  base::TimeDelta disk_writes_time_with_parallel_streams_;
+  base::TimeDelta disk_writes_time_without_parallel_streams_;
 
   std::vector<DownloadItem::ReceivedSlice> received_slices_;