Move ImportantFileWriter to base/. It now has two consumers, base/prefs and chrome/.

base/base.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'includes': [
     '../build/win_precompile.gypi',
@@ skipping 378 matching lines @@
         'debug/trace_event_unittest.cc',
         'debug/trace_event_unittest.h',
         'debug/trace_event_win_unittest.cc',
         'environment_unittest.cc',
         'file_descriptor_shuffle_unittest.cc',
         'file_path_unittest.cc',
         'file_util_proxy_unittest.cc',
         'file_util_unittest.cc',
         'file_version_info_unittest.cc',
         'files/dir_reader_posix_unittest.cc',
+        'files/important_file_writer_unittest.cc',
         'gmock_unittest.cc',
         'guid_unittest.cc',
         'hi_res_timer_manager_unittest.cc',
         'id_map_unittest.cc',
         'i18n/break_iterator_unittest.cc',
         'i18n/char_iterator_unittest.cc',
         'i18n/case_conversion_unittest.cc',
         'i18n/file_util_icu_unittest.cc',
         'i18n/icu_string_conversions_unittest.cc',
         'i18n/number_formatting_unittest.cc',
@@ skipping 647 matching lines @@
             'base_unittests.isolate',
           ],
           'sources': [
             'base_unittests.isolate',
           ],
         },
       ],
     }],
   ],
 }