Add more UMA to record whether parallel download is completed/interrupted/cancelled

content/browser/download/download_stats.h

Index: content/browser/download/download_stats.h
diff --git a/content/browser/download/download_stats.h b/content/browser/download/download_stats.h
index 0ecbf0cc6a6b2fef3e23d95198bcd6853842bd43..9de3d2b2a59262a8c98e1e57960ff0b193f9affb 100644
--- a/content/browser/download/download_stats.h
+++ b/content/browser/download/download_stats.h
@@ -91,12 +91,33 @@ enum DownloadCountTypes {
   // candidates for partial resumption.
   STRONG_VALIDATOR_AND_ACCEPTS_RANGES,
 
-  // Count of downloads that uses parallel download requests.
+  // (Deprecated) Count of downloads that uses parallel download requests. Use
+  // PARALLEL_DOWNLOAD_START_COUNT instead.
   USES_PARALLEL_REQUESTS,

[David Trainor- moved to gerrit, 2017/03/23 21:43:07]

DOWNLOAD_COUNT_UNUSED_18?

[qinmin, 2017/03/23 21:52:47]

i am wondering whether i can remove this, this is not used since the finch trial
hasn't started yet.

 
   DOWNLOAD_COUNT_TYPES_LAST_ENTRY
 };
 
+// Enums for Download.ParallelDownloadCounts.
+enum ParallelDownloadCountTypes {
+  // Downloads that actually complete.
+  PARALLEL_DOWNLOAD_COMPLETED_COUNT,

[David Trainor- moved to gerrit, 2017/03/23 21:43:07]

How many of these will double count with the non-parallel case?  Will we be able
to easily distinguish stats for normal vs. parallel downloads?

[qinmin, 2017/03/23 21:52:47]

Not sure exact percentage, but we should expect similar stats for Completed,
cancelled. 
The started count will tell us the double count case.
I would expect interrupted_count to go up a little bit, but not too much.

+
+  // Downloads that are cancelled before completion (user action or error).
+  PARALLEL_DOWNLOAD_CANCELLED_COUNT,
+
+  // Downloads that are started.
+  PARALLEL_DOWNLOAD_START_COUNT,
+
+  // Downloads that were interrupted by the OS.
+  PARALLEL_DOWNLOAD_INTERRUPTED_COUNT,
+
+  // Counts interruptions that happened at the end of the download.
+  PARALLEL_DOWNLOAD_INTERRUPTED_AT_END_COUNT,
+
+  PARALLEL_DOWNLOAD_COUNT_TYPES_LAST_ENTRY
+};
+
 enum DownloadSource {
   // The download was initiated when the SavePackage system rejected
   // a Save Page As ... by returning false from
@@ -149,7 +170,8 @@ void RecordDownloadCompleted(const base::TimeTicks& start,
 // Record INTERRUPTED_COUNT, |reason|, |received| and |total| bytes.
 void RecordDownloadInterrupted(DownloadInterruptReason reason,
                                int64_t received,
-                               int64_t total);
+                               int64_t total,
+                               bool uses_parallel_requests);
 
 // Record that a download has been classified as malicious.
 void RecordMaliciousDownloadClassified(DownloadDangerType danger_type);
@@ -205,6 +227,9 @@ void RecordFileBandwidth(size_t length,
                          base::TimeDelta disk_write_time,
                          base::TimeDelta elapsed_time);
 
+// Increment one of the count for parallel download.
+void RecordParallelDownloadCount(ParallelDownloadCountTypes type);
+
 // Records the bandwidth for parallel download and estimates the saved time at
 // the file end. Does not count in any hash computation or file open/close time.
 void RecordParallelDownloadStats(