Add UMA metric to track parallel download requests stats.

content/browser/download/download_stats.cc

 // Copyright (c) 2012 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/download_stats.h"
 
 #include "base/macros.h"
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/sparse_histogram.h"
@@ skipping 755 matching lines @@
   RecordBandwidthMetric(
       "Download.BandwidthDiskBytesPerSecond",
       CalculateBandwidthBytesPerSecond(length, disk_write_time));
 }
 
 void RecordParallelDownloadCount(DownloadCountTypes type) {
   UMA_HISTOGRAM_ENUMERATION("Download.Counts.ParallelDownload", type,
                             DOWNLOAD_COUNT_TYPES_LAST_ENTRY);
 }
 
+void RecordParallelDownloadRequestCount(int request_count) {
+  UMA_HISTOGRAM_CUSTOM_COUNTS("Download.ParallelDownloadRequestCount",
+                              request_count, 1, 10, 10);

[Ilya Sherman, 2017/03/31 00:33:04]

nit: Did you check that this gives you the desired bucket layout?  I suspect you
might want the last argument to be 11, to make space for the underflow bucket. 
In any case, I'd recommend double-checking locally via chrome://histograms that
this gives you the desired layout.

[xingliu, 2017/03/31 21:48:26]

Done, thanks.

+}
+
+void RecordParallelDownloadEarlyRequests(int request_count) {
+  UMA_HISTOGRAM_CUSTOM_COUNTS("Download.ParallelDownloadEarlyRequestCount",
+                              request_count, 1, 10, 10);
+}
+
+void RecordParallelDownloadAddStreamSuccess(bool success) {
+  UMA_HISTOGRAM_BOOLEAN("Download.ParallelDownloadAddStreamSuccess", success);
+}
+
 void RecordParallelDownloadStats(
     size_t bytes_downloaded_with_parallel_streams,
     base::TimeDelta time_with_parallel_streams,
     size_t bytes_downloaded_without_parallel_streams,
     base::TimeDelta time_without_parallel_streams) {
   int bandwidth_without_parallel_streams = CalculateBandwidthBytesPerSecond(
       bytes_downloaded_without_parallel_streams, time_without_parallel_streams);
   RecordBandwidthMetric(
       "Download.BandwidthWithoutParallelStreamsBytesPerSecond",
       bandwidth_without_parallel_streams);
@@ skipping 99 matching lines @@
   if (!page_transition)
     return;
 
   UMA_HISTOGRAM_ENUMERATION(
       "Download.PageTransition",
       ui::PageTransitionStripQualifier(page_transition.value()),
       ui::PAGE_TRANSITION_LAST_CORE + 1);
 }
 
 }  // namespace content