Update GN build files for new prefs location.

components/proxy_config/BUILD.gn

 # Copyright 2015 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.
 
 # GYP version: components/proxy_config.gypi:proxy_config
 component("proxy_config") {
   sources = [
     "pref_proxy_config_tracker.cc",
     "pref_proxy_config_tracker.h",
     "pref_proxy_config_tracker_impl.cc",
     "pref_proxy_config_tracker_impl.h",
     "proxy_config_dictionary.cc",
     "proxy_config_dictionary.h",
     "proxy_config_export.h",
     "proxy_config_pref_names.cc",
     "proxy_config_pref_names.h",
     "proxy_prefs.cc",
     "proxy_prefs.h",
   ]
 
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
   defines = [ "PROXY_CONFIG_IMPLEMENTATION" ]
 
   deps = [
     "//base",
-    "//base:prefs",
+    "//components/prefs",
     "//net",
     "//url",
   ]
 
   # TODO(https://crbug.com/562773): Break a header include cycle on ChromeOS
   # and disable include checking so GN doesn't complain about the missing
   # dependency (it still links OK). This cycle should be fixed and header
   # checking enabled.
   if (is_chromeos) {
     check_includes = false
   } else {
     deps += [ "//components/pref_registry" ]
   }
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "pref_proxy_config_tracker_impl_unittest.cc",
     "proxy_config_dictionary_unittest.cc",
     "proxy_prefs_unittest.cc",
   ]
   deps = [
     ":proxy_config",
     "//base",
-    "//base:prefs_test_support",
     "//base/test:test_support",
+    "//components/prefs:test_support",
     "//net",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }