Add a delay to send the parallel requests.

content/browser/download/parallel_download_utils.cc

 // Copyright 2017 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/parallel_download_utils.h"
 
 #include "base/metrics/field_trial_params.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/time/time.h"
 #include "content/public/browser/download_save_info.h"
 #include "content/public/common/content_features.h"
 
 namespace content {
 
 namespace {
 
 // Finch parameter key value for minimum slice size in bytes to use parallel
 // download.
 const char kMinSliceSizeFinchKey[] = "min_slice_size";
 
 // Default value for |kMinSliceSizeFinchKey|, when no parameter is specified.
 const int64_t kMinSliceSizeParallelDownload = 2097152;
 
 // Finch parameter key value for number of parallel requests in a parallel
 // download, including the original request.
 const char kParallelRequestCountFinchKey[] = "request_count";
 
 // Default value for |kParallelRequestCountFinchKey|, when no parameter is
 // specified.
 const int kParallelRequestCount = 2;
 
+// Finch parameter key value for the delay time in milliseconds to send
+// parallel requests after response of the original request is handled.
+const char kParallelRequestDelayFinchKey[] = "parallel_request_delay";
+
 // TODO(qinmin): replace this with a comparator operator in
 // DownloadItem::ReceivedSlice.
 bool compareReceivedSlices(const DownloadItem::ReceivedSlice& lhs,
                            const DownloadItem::ReceivedSlice& rhs) {
   return lhs.offset < rhs.offset;
 }
 
 }  // namespace
 
 std::vector<DownloadItem::ReceivedSlice> FindSlicesToDownload(
@@ skipping 42 matching lines @@
   }
 
   it = received_slices.emplace(it, new_slice);
   return static_cast<size_t>(std::distance(received_slices.begin(), it));
 }
 
 int64_t GetMinSliceSizeConfig() {
   std::string finch_value = base::GetFieldTrialParamValueByFeature(
       features::kParallelDownloading, kMinSliceSizeFinchKey);
   int64_t result;
-  return !finch_value.empty() && base::StringToInt64(finch_value, &result)
+  return base::StringToInt64(finch_value, &result)
              ? result
              : kMinSliceSizeParallelDownload;
 }
 
 int GetParallelRequestCountConfig() {
   std::string finch_value = base::GetFieldTrialParamValueByFeature(
       features::kParallelDownloading, kParallelRequestCountFinchKey);
   int result;
-  return !finch_value.empty() && base::StringToInt(finch_value, &result)
-             ? result
-             : kParallelRequestCount;
+  return base::StringToInt(finch_value, &result) ? result
+                                                 : kParallelRequestCount;
+}
+
+base::TimeDelta GetParallelRequestDelayConfig() {
+  std::string finch_value = base::GetFieldTrialParamValueByFeature(
+      features::kParallelDownloading, kParallelRequestDelayFinchKey);
+  int64_t time_ms = 0;
+  return base::StringToInt64(finch_value, &time_ms)
+             ? base::TimeDelta::FromMilliseconds(time_ms)
+             : base::TimeDelta::FromMilliseconds(0);
 }
 
 }  // namespace content