Update GN build files for new prefs location.

components/web_cache/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.
 
 source_set("browser") {
   sources = [
     "web_cache_manager.cc",
     "web_cache_manager.h",
   ]
 
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
   deps = [
     "//base",
-    "//base:prefs",
+    "//components/prefs",
     "//components/web_cache/common",
     "//content/public/browser",
     "//third_party/WebKit/public:blink",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "web_cache_manager_unittest.cc",
   ]
   deps = [
     ":browser",
     "//base",
     "//content/test:test_support",
     "//testing/gtest",
   ]
 }