Inline extensions .gypi files into GN build.

extensions/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/features.gni")
-import("//extensions/extensions.gni")
 
 assert(enable_extensions)
 
-# GYP version: extensions/extensions.gyp:extensions_utility
 source_set("utility") {
-  sources = rebase_path(extensions_gypi_values.extensions_utility_sources,
-                        ".",
-                        "//extensions")
+  sources = [
+    "unpacker.cc",
+    "unpacker.h",
+    "utility_handler.cc",
+    "utility_handler.h",
+  ]
 
   # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
   deps = [
     "//content/public/common",
     "//content/public/utility",
     "//extensions/common",
     "//skia",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "unpacker_unittest.cc",
   ]
   deps = [
     ":utility",
     "//base",
     "//extensions:test_support",
     "//extensions/common",
     "//extensions/strings",
     "//testing/gtest",
     "//third_party/zlib:zip",
     "//ui/base",
   ]
 }