Linux: Move base/mime_util* to base/nix. It's not used on any other platform.

base/base.gypi

 # Copyright (c) 2011 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.
 
 {
   'target_defaults': {
     'variables': {
       'base_target': 0,
     },
     'target_conditions': [
@@ skipping 175 matching lines @@
           'message_pump_default.cc',
           'message_pump_default.h',
           'message_pump_win.cc',
           'message_pump_win.h',
           'metrics/histogram.cc',
           'metrics/histogram.h',
           'metrics/stats_counters.cc',
           'metrics/stats_counters.h',
           'metrics/stats_table.cc',
           'metrics/stats_table.h',
-          'mime_util.h',
-          'mime_util_xdg.cc',
           'native_library.h',
           'native_library_linux.cc',
           'native_library_mac.mm',
           'native_library_win.cc',
           'observer_list.h',
           'observer_list_threadsafe.h',
           'os_compat_android.cc',
           'os_compat_android.h',
           'path_service.cc',
           'path_service.h',
@@ skipping 143 matching lines @@
           'utf_string_conversions.cc',
           'utf_string_conversions.h',
           'values.cc',
           'values.h',
           'value_conversions.cc',
           'value_conversions.h',
           'version.cc',
           'version.h',
           'vlog.cc',
           'vlog.h',
+          'nix/mime_util_xdg.cc',
+          'nix/mime_util_xdg.h',
           'nix/xdg_util.cc',
           'nix/xdg_util.h',
           'win/event_trace_consumer.h',
           'win/event_trace_controller.cc',
           'win/event_trace_controller.h',
           'win/event_trace_provider.cc',
           'win/event_trace_provider.h',
           'win/i18n.cc',
           'win/i18n.h',
           'win/iat_patch_function.cc',
@@ skipping 461 matching lines @@
             'third_party/xdg_mime/xdgmimemagic.c',
             'third_party/xdg_mime/xdgmimemagic.h',
             'third_party/xdg_mime/xdgmimeparent.c',
             'third_party/xdg_mime/xdgmimeparent.h',
           ],
         },
       ],
     }],
   ],
 }