Add the metric to record percentage improvement for parallel download.

content/browser/download/download_stats.cc

Index: content/browser/download/download_stats.cc
diff --git a/content/browser/download/download_stats.cc b/content/browser/download/download_stats.cc
index ed24173103d329447919b88f2719b61ad1ccbd6f..708615419d511191b4d563bd5c0584f514c90476 100644
--- a/content/browser/download/download_stats.cc
+++ b/content/browser/download/download_stats.cc
@@ -819,16 +819,34 @@ void RecordParallelizableDownloadStats(
 
   base::TimeDelta time_saved;
   if (bytes_downloaded_with_parallel_streams > 0) {
+    int64_t bandwidth_with_parallel_streams = CalculateBandwidthBytesPerSecond(
+        bytes_downloaded_with_parallel_streams, time_with_parallel_streams);
     RecordBandwidthMetric(
         "Download.ParallelizableDownloadBandwidth."
         "WithParallelRequestsMultipleStreams",
-        CalculateBandwidthBytesPerSecond(bytes_downloaded_with_parallel_streams,
-                                         time_with_parallel_streams));
+        bandwidth_with_parallel_streams);
     if (bandwidth_without_parallel_streams > 0) {
       time_saved = base::TimeDelta::FromMilliseconds(
                        1000.0 * bytes_downloaded_with_parallel_streams /
                        bandwidth_without_parallel_streams) -
                    time_with_parallel_streams;
+      int bandwidth_ratio_percentage =
+          (100.0 * bandwidth_with_parallel_streams) /
+          bandwidth_without_parallel_streams;
+      UMA_HISTOGRAM_CUSTOM_COUNTS(
+          "Download.ParallelDownload.BandwidthRatioPercentage",
+          bandwidth_ratio_percentage, 0, 400, 101);
+      base::TimeDelta total_time =
+          time_with_parallel_streams + time_without_parallel_streams;
+      size_t total_size = bytes_downloaded_with_parallel_streams +
+                          bytes_downloaded_without_parallel_streams;
+      base::TimeDelta non_parallel_time = base::TimeDelta::FromSecondsD(
+          static_cast<double>(total_size) / bandwidth_without_parallel_streams);
+      int time_ratio_percentage =
+          100.0 * total_time.InSecondsF() / non_parallel_time.InSecondsF();
+      UMA_HISTOGRAM_CUSTOM_COUNTS(
+          "Download.ParallelDownload.TotalTimeRatioPercentage",
+          time_ratio_percentage, 0, 200, 101);
     }
   }