Add CSS variables feature flag to chrome://flags.

chrome/browser/about_flags.cc

 // Copyright (c) 2012 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/browser/about_flags.h"
 
 #include <algorithm>
 #include <iterator>
 #include <map>
 #include <set>
@@ skipping 592 matching lines @@
     SINGLE_VALUE_TYPE(switches::kEnableStyleScoped)
   },
   {
     "enable-css-regions",
     IDS_FLAGS_CSS_REGIONS_NAME,
     IDS_FLAGS_CSS_REGIONS_DESCRIPTION,
     kOsAll,
     SINGLE_VALUE_TYPE(switches::kEnableCssRegions)
   },
   {
+    "enable-css-variables",
+    IDS_FLAGS_CSS_VARIABLES_NAME,
+    IDS_FLAGS_CSS_VARIABLES_DESCRIPTION,
+    kOsAll,
+    SINGLE_VALUE_TYPE(switches::kEnableCssVariables)
+  },
+  {
     "enable-extension-activity-ui",
     IDS_FLAGS_ENABLE_EXTENSION_ACTIVITY_UI_NAME,
     IDS_FLAGS_ENABLE_EXTENSION_ACTIVITY_UI_DESCRIPTION,
     kOsAll,
     SINGLE_VALUE_TYPE(switches::kEnableExtensionActivityUI)
   },
   {
     "disable-ntp-other-sessions-menu",
     IDS_FLAGS_NTP_OTHER_SESSIONS_MENU_NAME,
     IDS_FLAGS_NTP_OTHER_SESSIONS_MENU_DESCRIPTION,
@@ skipping 668 matching lines @@
 }
 
 const Experiment* GetExperiments(size_t* count) {
   *count = num_experiments;
   return experiments;
 }
 
 }  // namespace testing
 
 }  // namespace about_flags