Add new UMA stats for parallelizable download

content/browser/download/download_job_factory.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/download_job_factory.h"
 
 #include <memory>
 
 #include "base/memory/ptr_util.h"
 #include "content/browser/download/download_item_impl.h"
 #include "content/browser/download/download_job.h"
 #include "content/browser/download/download_job_impl.h"
 #include "content/browser/download/download_stats.h"
 #include "content/browser/download/parallel_download_job.h"
 #include "content/browser/download/parallel_download_utils.h"
 #include "content/public/common/content_features.h"
 
 namespace content {
 
 namespace {
 
-// Returns if the download should be a parallel download.
+// Returns if the download can be parallelized.
 bool ShouldUseParallelDownload(const DownloadCreateInfo& create_info) {

[xingliu, 2017/04/19 02:18:11]

nit: Maybe also change the function name?

[qinmin, 2017/04/19 22:42:33]

Done.

   // To enable parallel download, following conditions need to be satisfied.
   // 1. Feature |kParallelDownloading| enabled.
   // 2. Strong validators response headers. i.e. ETag and Last-Modified.
   // 3. Accept-Ranges header.
   // 4. Content-Length header.
   // 5. Content-Length is no less than the minimum slice size configuration.
   // 6. HTTP/1.1 protocol, not QUIC nor HTTP/1.0.
-  if (!base::FeatureList::IsEnabled(features::kParallelDownloading))
-    return false;
 
   // Etag and last modified are stored into DownloadCreateInfo in
   // DownloadRequestCore only if the response header complies to the strong
   // validator rule.
   bool has_strong_validator =
       !create_info.etag.empty() || !create_info.last_modified.empty();
   bool has_content_length = create_info.total_bytes > 0;
   bool satisfy_min_file_size =
       create_info.total_bytes >= GetMinSliceSizeConfig();
   bool satisfy_connection_type = create_info.connection_info ==
                                  net::HttpResponseInfo::CONNECTION_INFO_HTTP1_1;
 
   bool should_use_parallel_download =
       has_strong_validator && create_info.accept_range && has_content_length &&
       satisfy_min_file_size && satisfy_connection_type;
 
+  if (!base::FeatureList::IsEnabled(features::kParallelDownloading))
+    return should_use_parallel_download;
+
   RecordParallelDownloadCreationEvent(
       should_use_parallel_download
           ? ParallelDownloadCreationEvent::STARTED_PARALLEL_DOWNLOAD
           : ParallelDownloadCreationEvent::FELL_BACK_TO_NORMAL_DOWNLOAD);
 
   if (!has_strong_validator) {
     RecordParallelDownloadCreationEvent(
         ParallelDownloadCreationEvent::FALLBACK_REASON_STRONG_VALIDATORS);
   }
   if (!create_info.accept_range) {
@@ skipping 15 matching lines @@
 
   return should_use_parallel_download;
 }
 
 }  // namespace
 
 std::unique_ptr<DownloadJob> DownloadJobFactory::CreateJob(
     DownloadItemImpl* download_item,
     std::unique_ptr<DownloadRequestHandleInterface> req_handle,
     const DownloadCreateInfo& create_info) {
+  bool is_parallizable = ShouldUseParallelDownload(create_info);
   // Build parallel download job.
-  if (ShouldUseParallelDownload(create_info)) {
+  if (base::FeatureList::IsEnabled(features::kParallelDownloading) &&
+      is_parallizable) {
     return base::MakeUnique<ParallelDownloadJob>(download_item,
                                                  std::move(req_handle),
                                                  create_info);
   }
 
   // An ordinary download job.
-  return base::MakeUnique<DownloadJobImpl>(download_item,
-                                           std::move(req_handle));
+  return base::MakeUnique<DownloadJobImpl>(download_item, std::move(req_handle),
+                                           is_parallizable);
 }
 
 }  // namespace