Add UMA to track why a download is non-parallel when enabled parallel

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 798 matching lines @@
     UMA_HISTOGRAM_CUSTOM_COUNTS(
         "Download.EstimatedTimeSavedWithParallelDownload",
         time_saved.InMilliseconds(), 0, kMillisecondsPerHour, 50);
   } else {
     UMA_HISTOGRAM_CUSTOM_COUNTS(
         "Download.EstimatedTimeWastedWithParallelDownload",
         -time_saved.InMilliseconds(), 0, kMillisecondsPerHour, 50);
   }
 }
 
+void RecordParallelDownloadCreationEvent(ParallelDownloadCreationEvent event) {
+  UMA_HISTOGRAM_ENUMERATION("Download.ParallelDownload.CreationEvent", event,
+                            ParallelDownloadCreationEvent::COUNT);
+}
+
 void RecordDownloadFileRenameResultAfterRetry(
     base::TimeDelta time_since_first_failure,
     DownloadInterruptReason interrupt_reason) {
   if (interrupt_reason == DOWNLOAD_INTERRUPT_REASON_NONE) {
     UMA_HISTOGRAM_TIMES("Download.TimeToRenameSuccessAfterInitialFailure",
                         time_since_first_failure);
   } else {
     UMA_HISTOGRAM_TIMES("Download.TimeToRenameFailureAfterInitialFailure",
                         time_since_first_failure);
   }
@@ skipping 64 matching lines @@
   if (!page_transition)
     return;
 
   UMA_HISTOGRAM_ENUMERATION(
       "Download.PageTransition",
       ui::PageTransitionStripQualifier(page_transition.value()),
       ui::PAGE_TRANSITION_LAST_CORE + 1);
 }
 
 }  // namespace content