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

content/app/content_main_runner.cc

Index: content/app/content_main_runner.cc
diff --git a/content/app/content_main_runner.cc b/content/app/content_main_runner.cc
index 2a511cbe1303cdd33d64cdf297146df22e08341f..f6c00f3db4dca275b810a91a42a7e0de81e4254e 100644
--- a/content/app/content_main_runner.cc
+++ b/content/app/content_main_runner.cc
@@ -664,16 +664,6 @@ class ContentMainRunnerImpl : public ContentMainRunner {
     std::string process_type =
         command_line.GetSwitchValueASCII(switches::kProcessType);
 
-    // --enable-network-service requires both --enable-browser-side-navigation
-    // (PlzNavigate) and the LoadingWithMojo feature.
-    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-            switches::kEnableNetworkService)) {
-      base::CommandLine::ForCurrentProcess()->AppendSwitch(
-          switches::kEnableBrowserSideNavigation);
-      base::CommandLine::ForCurrentProcess()->AppendSwitchASCII(
-          switches::kEnableFeatures, features::kLoadingWithMojo.name);
-    }
-
     // Run this logic on all child processes. Zygotes will run this at a later
     // point in time when the command line has been updated.
     std::unique_ptr<base::FieldTrialList> field_trial_list;