Move enable extensions define to a build flag.

components/content_settings/core/browser/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/features.gni")
 
 static_library("browser") {
   sources = [
     "content_settings_binary_value_map.cc",
     "content_settings_binary_value_map.h",
@@ skipping 33 matching lines @@
     "website_settings_registry.h",
   ]
 
   deps = [
     "//base",
     "//components/content_settings/core/common",
     "//components/keyed_service/core",
     "//components/pref_registry:pref_registry",
     "//components/prefs",
     "//components/url_formatter",
+    "//extensions/features",
     "//net",
     "//url",
   ]
 
   configs += [
     "//build/config/compiler:no_size_t_to_int_warning",
     "//build/config/compiler:wexit_time_destructors",
   ]
 }
 
@@ skipping 14 matching lines @@
   }
 
   deps = [
     ":browser",
     "//base",
     "//base/test:test_support",
     "//components/content_settings/core/common",
     "//components/content_settings/core/test:test_support",
     "//components/pref_registry:test_support",
     "//components/prefs",
+    "//extensions/features",
     "//testing/gtest",
     "//url",
   ]
 }