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

content/public/common/content_features.cc

 // Copyright 2015 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 "build/build_config.h"
 #include "content/public/common/content_features.h"
 
 namespace features {
 
 // All features in alphabetical order.
@@ skipping 136 matching lines @@
     "MediaStreamOldAudioConstraints", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables the memory coordinator.
 // WARNING:
 // The memory coordinator is not ready for use and enabling this may cause
 // unexpected memory regression at this point. Please do not enable this.
 const base::Feature kMemoryCoordinator {
   "MemoryCoordinator", base::FEATURE_DISABLED_BY_DEFAULT
 };
 
+// Enables the network service.
+const base::Feature kNetworkService{"NetworkService",
+                                    base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Kill switch for Web Notification content images.
 const base::Feature kNotificationContentImage{"NotificationContentImage",
                                               base::FEATURE_ENABLED_BY_DEFAULT};
 // An experiment forcing events to be non-blocking when the main thread is
 // deemed unresponsive.  See crbug.com/599609.
 const base::Feature kMainThreadBusyScrollIntervention{
     "MainThreadBusyScrollIntervention", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Blob mojofication.
 const base::Feature kMojoBlobs{"MojoBlobs", base::FEATURE_DISABLED_BY_DEFAULT};
@@ skipping 232 matching lines @@
 #endif
 
 #if defined(OS_MACOSX)
 // The V2 sandbox on MacOS removes the unsandboed warmup phase and sandboxes the
 // entire life of the process.
 const base::Feature kMacV2Sandbox{"MacV2Sandbox",
                                   base::FEATURE_DISABLED_BY_DEFAULT};
 #endif  // defined(OS_MACOSX)
 
 }  // namespace features