Add a feature flag for network service and about:flags entry for it.

content/common/service_worker/service_worker_utils.cc

Index: content/common/service_worker/service_worker_utils.cc
diff --git a/content/common/service_worker/service_worker_utils.cc b/content/common/service_worker/service_worker_utils.cc
index 805644e74c030c77fc93474a684ce6002d6abb5e..0c87998ad56c9ad035b7eff0622e219b67783e87 100644
--- a/content/common/service_worker/service_worker_utils.cc
+++ b/content/common/service_worker/service_worker_utils.cc
@@ -10,6 +10,7 @@
 #include "base/logging.h"
 #include "base/strings/string_util.h"
 #include "content/public/common/browser_side_navigation_policy.h"
+#include "content/public/common/content_features.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/origin_util.h"
 
@@ -137,8 +138,7 @@ bool ServiceWorkerUtils::AllOriginsMatchAndCanAccessServiceWorkers(
 // static
 bool ServiceWorkerUtils::IsServicificationEnabled() {
   return IsBrowserSideNavigationEnabled() &&
-         base::CommandLine::ForCurrentProcess()->HasSwitch(
-             switches::kEnableNetworkService);
+         base::FeatureList::IsEnabled(features::kNetworkService);
 }
 
 // static