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

chrome/chrome_common.gypi

 # 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.
 
 {
   'targets': [
     {
       'target_name': 'common',
       'type': 'static_library',
       'variables': {
@@ skipping 198 matching lines @@
         'common/favicon_url.h',
         'common/form_data.cc',
         'common/form_data.h',
         'common/form_data_predictions.cc',
         'common/form_data_predictions.h',
         'common/form_field_data.cc',
         'common/form_field_data.h',
         'common/form_field_data_predictions.cc',
         'common/form_field_data_predictions.h',
         'common/icon_messages.h',
-        'common/important_file_writer.cc',
-        'common/important_file_writer.h',
         'common/instant_types.cc',
         'common/instant_types.h',
         'common/json_schema_constants.cc',
         'common/json_schema_constants.h',
         'common/json_schema_validator.cc',
         'common/json_schema_validator.h',
         'common/jstemplate_builder.cc',
         'common/jstemplate_builder.h',
         'common/localized_error.cc',
         'common/localized_error.h',
@@ skipping 357 matching lines @@
         'common/metrics/proto/user_action_event.proto',
       ],
       'variables': {
         'proto_in_dir': 'common/metrics/proto',
         'proto_out_dir': 'chrome/common/metrics/proto',
       },
       'includes': [ '../build/protoc.gypi' ],
     },
   ],
 }