Move enable extensions define to a build flag.

chrome/utility/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/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/sysroot.gni")
+import("//extensions/features/features.gni")
 import("//printing/features/features.gni")
 
 static_library("utility") {
   sources = [
     "chrome_content_utility_client.cc",
     "chrome_content_utility_client.h",
     "chrome_content_utility_ipc_whitelist.cc",
     "chrome_content_utility_ipc_whitelist.h",
     "cloud_print/bitmap_image.cc",
     "cloud_print/bitmap_image.h",
@@ skipping 24 matching lines @@
     "//chrome/common",
     "//chrome/common:mojo_bindings",
     "//components/safe_json/utility",
     "//components/search_engines",
     "//components/strings",
     "//components/url_formatter",
     "//content/public/child",
     "//content/public/common",
     "//content/public/utility",
     "//courgette:courgette_lib",
+    "//extensions/features",
     "//media",
     "//net:net_with_v8",
     "//printing/features",
     "//services/service_manager/public/cpp",
     "//skia",
     "//sql",
     "//third_party/libxml",
   ]
 
   if (!is_android) {
@@ skipping 108 matching lines @@
     sources -= [
       "printing_handler.cc",
       "printing_handler.h",
     ]
   }
 
   if (is_mac && safe_browsing_mode == 1) {
     deps += [ "//chrome/utility/safe_browsing/mac" ]
   }
 }