[PassKit refactoring] Added kNewPassKitDownload to chrome://flags.

Bug: 787943
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I332dac25551ae39094356846121e835faf3dceeb
Reviewed-on: https://chromium-review.googlesource.com/818077
Commit-Queue: Eugene But <eugenebut@chromium.org>
Reviewed-by: Gregory Chatzinoff <gchatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523464}

ios/chrome/browser/about_flags.mm

@@ -181,6 +181,9 @@ const flags_ui::FeatureEntry kFeatureEntries[] = {
     {"slim-navigation-manager", flag_descriptions::kSlimNavigationManagerName,
      flag_descriptions::kSlimNavigationManagerDescription, flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(web::features::kSlimNavigationManager)},
+    {"new-pass-kit-download", flag_descriptions::kNewPassKitDownloadName,
+     flag_descriptions::kNewPassKitDownloadDescription, flags_ui::kOsIos,
+     FEATURE_VALUE_TYPE(web::features::kNewPassKitDownload)},
     {"ios-share-canonical-url", flag_descriptions::kShareCanonicalURLName,
      flag_descriptions::kShareCanonicalURLDescription, flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(activity_services::kShareCanonicalURL)},