components: Make user_prefs a source_set.

components/user_prefs.gypi

 # Copyright (c) 2013 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.
 
 {
   'targets': [
     {
       'target_name': 'user_prefs',
-      'type': '<(component)',
+      'type': 'static_library',
       'dependencies': [
         '../base/base.gyp:base',
         '../base/base.gyp:base_prefs',
       ],
       'include_dirs': [
         '..',
       ],
-      'defines': [
-        'USER_PREFS_IMPLEMENTATION',
-      ],
       'sources': [
         'user_prefs/user_prefs.cc',
         'user_prefs/user_prefs.h',
-        'user_prefs/user_prefs_export.h',
       ],
     },
   ],
 }