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

content/browser/frame_host/render_frame_host_impl.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/frame_host/render_frame_host_impl.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 3179 matching lines @@
     DCHECK(!GetParent());
     render_view_host()->Send(new FrameMsg_EnableViewSourceMode(routing_id_));
   }
 
   const GURL body_url = body.get() ? body->GetURL() : GURL();
   const ResourceResponseHead head = response ?
       response->head : ResourceResponseHead();
   FrameMsg_CommitDataNetworkService_Params commit_data;
   commit_data.handle = handle.release();
   // TODO(scottmg): Pass a factory for SW, etc. once we have one.
-  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kEnableNetworkService)) {
+  if (base::FeatureList::IsEnabled(features::kNetworkService)) {
     if (!subresource_url_loader_factory_info.is_valid()) {
       const auto& schemes = URLDataManagerBackend::GetWebUISchemes();
       if (std::find(schemes.begin(), schemes.end(),
                     common_params.url.scheme()) != schemes.end()) {
         commit_data.url_loader_factory = CreateWebUIURLLoader(frame_tree_node_)
                                              .PassInterface()
                                              .PassHandle()
                                              .release();
       }
     } else {
@@ skipping 933 matching lines @@
 }
 
 void RenderFrameHostImpl::ForwardGetInterfaceToRenderFrame(
     const std::string& interface_name,
     mojo::ScopedMessagePipeHandle pipe) {
   GetRemoteInterfaces()->GetInterface(interface_name, std::move(pipe));
 }
 #endif
 
 }  // namespace content