Add support for extensions_unittests to the GN build

extensions/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/crypto.gni")
 import("//build/config/features.gni")
 
 # GYP version: extensions/extensions.gyp:extensions_browser
 source_set("browser") {
   sources = []
@@ skipping 536 matching lines @@
       "warning_service.h",
       "warning_service_factory.cc",
       "warning_service_factory.h",
       "warning_set.cc",
       "warning_set.h",
     ]
 
     deps += [
       "//components/onc",
       "//components/storage_monitor",
+      "//components/update_client",
       "//crypto:platform",
       "//device/bluetooth",
       "//device/core",
       "//device/hid",
       "//device/serial",
       "//device/usb",
       "//extensions/common/api/cast_channel:cast_channel_proto",
     ]
 
     if (is_chromeos) {
@@ skipping 44 matching lines @@
         "api/networking_private/networking_private_service_client.cc",
         "api/networking_private/networking_private_service_client.h",
       ]
     }
   }
 
   if (is_win) {
     cflags = [ "/wd4267" ]  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
   }
 }