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

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 432 matching lines @@
         'json/json_value_converter_unittest.cc',
         'json/json_value_serializer_unittest.cc',
         'json/json_writer_unittest.cc',
         'json/string_escape_unittest.cc',
         'lazy_instance_unittest.cc',
         'logging_unittest.cc',
         'mac/bind_objc_block_unittest.mm',
         'mac/call_with_eh_frame_unittest.mm',
         'mac/dispatch_source_mach_unittest.cc',
         'mac/foundation_util_unittest.mm',
-        'mac/libdispatch_task_runner_unittest.cc',
         'mac/mac_util_unittest.mm',
         'mac/mach_port_broker_unittest.cc',
         'mac/objc_property_releaser_unittest.mm',
         'mac/scoped_nsobject_unittest.mm',
         'mac/scoped_objc_class_swizzler_unittest.mm',
         'mac/scoped_sending_event_unittest.mm',
         'md5_unittest.cc',
         'memory/aligned_memory_unittest.cc',
         'memory/discardable_shared_memory_unittest.cc',
         'memory/linked_ptr_unittest.cc',
@@ skipping 1323 matching lines @@
                 ['include', 'mac/bind_objc_block_unittest_arc\\.mm$'],
                 ['include', 'mac/scoped_nsobject_unittest_arc\\.mm$'],
               ],
             }]
           ],
         },
       ],
     }],
   ],
 }