Update GN build files for new prefs location.

ios/chrome/test/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.
 
 source_set("test") {
   testonly = true
   sources = [
     "block_cleanup_test.h",
     "block_cleanup_test.mm",
     "ios_chrome_scoped_testing_chrome_browser_provider.cc",
     "ios_chrome_scoped_testing_chrome_browser_provider.h",
     "ios_chrome_scoped_testing_local_state.cc",
     "ios_chrome_scoped_testing_local_state.h",
     "ios_chrome_unit_test_suite.cc",
     "ios_chrome_unit_test_suite.h",
     "run_all_unittests.cc",
     "testing_application_context.cc",
     "testing_application_context.h",
   ]
 
   deps = [
     "//base",
-    "//base:prefs",
     "//components/network_time",
+    "//components/prefs",
     "//ios/chrome/browser",
     "//ios/public/provider/chrome/browser",
     "//ios/public/test",
     "//ios/web",
     "//testing/gmock",
     "//testing/gtest",
     "//ui/base",
     "//url",
   ]
 }