Put STHSet component behind a base::Feature.

chrome/common/chrome_features.cc

 // Copyright 2016 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 "chrome/common/chrome_features.h"
 
 namespace features {
 
 // All features in alphabetical order.
 
@@ skipping 60 matching lines @@
 #endif  // defined(OS_CHROMEOS)
 
 const base::Feature kSafeSearchUrlReporting{"SafeSearchUrlReporting",
                                             base::FEATURE_DISABLED_BY_DEFAULT};
 
 // A new user experience for transitioning into fullscreen and mouse pointer
 // lock states.
 const base::Feature kSimplifiedFullscreenUI{"ViewsSimplifiedFullscreenUI",
                                             base::FEATURE_ENABLED_BY_DEFAULT};
 
+// Enables or disables the STH component-updater component.
+const base::Feature kSTHSetComponent{"STHSetComponent",
+                                     base::FEATURE_ENABLED_BY_DEFAULT};
+
 #if defined(SYZYASAN)
 // Enable the deferred free mechanism in the syzyasan module, which helps the
 // performance by deferring some work on the critical path to a background
 // thread.
 const base::Feature kSyzyasanDeferredFree{"SyzyasanDeferredFree",
                                           base::FEATURE_DISABLED_BY_DEFAULT};
 #endif
 
 #if defined(OS_CHROMEOS)
 // Enables or disables the opt-in IME menu in the language settings page.
 const base::Feature kOptInImeMenu{"OptInImeMenu",
                                   base::FEATURE_DISABLED_BY_DEFAULT};
 #endif  // defined(OS_CHROMEOS)
 
 }  // namespace features