[Mac/GN] Add missing -Wobjc-missing-property-synthesis.

third_party/class-dump/BUILD.gn

 # Copyright 2016 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.
 
 config("config") {
   visibility = [ ":class-dump" ]
   libs = [ "Foundation.framework" ]
 
   # TODO(crbug.com/595295): Building class-dump tools requires OS X SDK
   # version 10.9 or higher. Remove this override once the global version
@@ skipping 163 matching lines @@
     "src/Source/NSScanner-CDExtensions.h",
     "src/Source/NSScanner-CDExtensions.m",
     "src/Source/NSString-CDExtensions.h",
     "src/Source/NSString-CDExtensions.m",
     "src/Source/ULEB128.h",
     "src/Source/ULEB128.m",
     "src/Source/cd_objc2.h",
     "src/class-dump.m",
   ]
 
+  configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     ":config",
     "//build/config/compiler:enable_arc",
     "//build/config/compiler:no_chromium_code",
   ]
 
   # TODO(crbug.com/595295): Building class-dump tools requires OS X SDK
   # version 10.9 or higher. To prevent mixing code using different value
   # of minimum SDK supported, forbids dependencies on any Chromium target.
   assert_no_deps = [ "//base/*" ]
 }