[Android] Add an about flag for Download Manager UI

chrome/browser/android/chrome_feature_list.cc

Index: chrome/browser/android/chrome_feature_list.cc
diff --git a/chrome/browser/android/chrome_feature_list.cc b/chrome/browser/android/chrome_feature_list.cc
index 3f71d128da452c97e7eb7961b9bdded3072e9e72..6417513ea06fe8f5fcc634ddb4ec10ab7260356a 100644
--- a/chrome/browser/android/chrome_feature_list.cc
+++ b/chrome/browser/android/chrome_feature_list.cc
@@ -35,6 +35,7 @@ const base::Feature* kFeaturesExposedToJava[] = {
     &features::kSimplifiedFullscreenUI,
     &features::kWebPayments,
     &kAllBookmarksFeature,
+    &kDownloadsUiFeature,
     &kAndroidPayIntegrationV1,
     &kImportantSitesInCBD,
     &ntp_snippets::kContentSuggestionsFeature,
@@ -58,6 +59,9 @@ const base::Feature* kFeaturesExposedToJava[] = {
 const base::Feature kAllBookmarksFeature{"AllBookmarks",
                                          base::FEATURE_ENABLED_BY_DEFAULT};
 
+const base::Feature kDownloadsUiFeature{"DownloadsUi",
+                                         base::FEATURE_ENABLED_BY_DEFAULT};
+
 const base::Feature kImportantSitesInCBD{"ImportantSitesInCBD",
                                          base::FEATURE_DISABLED_BY_DEFAULT};