add a download slices table into history download db

chrome/common/chrome_features.cc

Index: chrome/common/chrome_features.cc
diff --git a/chrome/common/chrome_features.cc b/chrome/common/chrome_features.cc
index c168f8488fec38b977c0eb1091c7dddab95581a7..e32a968df77d793284a58520383b364abea45983 100644
--- a/chrome/common/chrome_features.cc
+++ b/chrome/common/chrome_features.cc
@@ -173,9 +173,6 @@ const base::Feature kOfflinePageDownloadSuggestionsFeature{
 const base::Feature kOverrideYouTubeFlashEmbed{
     "OverrideYouTubeFlashEmbed", base::FEATURE_ENABLED_BY_DEFAULT};
 
-const base::Feature kParallelDownloading{
-    "ParallelDownloading", base::FEATURE_DISABLED_BY_DEFAULT};
-
 // Enables Permissions Blacklisting via Safe Browsing.
 const base::Feature kPermissionsBlacklist{
     "PermissionsBlacklist", base::FEATURE_DISABLED_BY_DEFAULT};