Remove base::mac::LibDispatchTaskRunner and migrate its sole client to plain libdispatch.

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.
 
 {
   'includes': [
     'trace_event/trace_event.gypi',
   ],
   'target_defaults': {
     'variables': {
@@ skipping 279 matching lines @@
           'mac/close_nocancel.cc',
           'mac/cocoa_protocols.h',
           'mac/dispatch_source_mach.cc',
           'mac/dispatch_source_mach.h',
           'mac/foundation_util.h',
           'mac/foundation_util.mm',
           'mac/launch_services_util.cc',
           'mac/launch_services_util.h',
           'mac/launchd.cc',
           'mac/launchd.h',
-          'mac/libdispatch_task_runner.cc',
-          'mac/libdispatch_task_runner.h',
           'mac/mac_logging.h',
           'mac/mac_logging.mm',
           'mac/mac_util.h',
           'mac/mac_util.mm',
           'mac/mach_logging.cc',
           'mac/mach_logging.h',
           'mac/mach_port_broker.h',
           'mac/mach_port_broker.mm',
           'mac/mach_port_util.cc',
           'mac/mach_port_util.h',
@@ skipping 786 matching lines @@
           'i18n/time_formatting.h',
           'i18n/timezone.cc',
           'i18n/timezone.h',
           'i18n/utf8_validator_tables.cc',
           'i18n/utf8_validator_tables.h',
         ],
       }]
     ],
   },
 }