Make MessageLoopProxy::current() usable on threads that don't have MessageLoop.

base/base.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.
 
 {
   'target_defaults': {
     'variables': {
       'base_target': 0,
     },
     'target_conditions': [
@@ skipping 261 matching lines @@
           'sequenced_task_runner.cc',
           'sequenced_task_runner.h',
           'sequenced_task_runner_helpers.h',
           'sha1.h',
           'sha1_portable.cc',
           'sha1_win.cc',
           'shared_memory.h',
           'shared_memory_android.cc',
           'shared_memory_posix.cc',
           'shared_memory_win.cc',
+          'single_thread_task_runner.cc',
           'single_thread_task_runner.h',
           'stack_container.h',
           'stl_util.h',
           'string_number_conversions.cc',
           'string_number_conversions.h',
           'string_piece.cc',
           'string_piece.h',
           'string_split.cc',
           'string_split.h',
           'string_tokenizer.h',
@@ skipping 626 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',
           ],
         },
       ],
     }],
   ],
 }