Add POSIX shared memory support for Mac

base/BUILD.gn

 # Copyright (c) 2013 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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 493 matching lines @@
     "memory/ref_counted_delete_on_message_loop.h",
     "memory/ref_counted_memory.cc",
     "memory/ref_counted_memory.h",
     "memory/scoped_policy.h",
     "memory/scoped_vector.h",
     "memory/shared_memory.h",
     "memory/shared_memory_android.cc",
     "memory/shared_memory_handle.h",
     "memory/shared_memory_handle_mac.cc",
     "memory/shared_memory_handle_win.cc",
+    "memory/shared_memory_helper.cc",
+    "memory/shared_memory_helper.h",
     "memory/shared_memory_mac.cc",
     "memory/shared_memory_nacl.cc",
     "memory/shared_memory_posix.cc",
     "memory/shared_memory_win.cc",
     "memory/singleton.cc",
     "memory/singleton.h",
     "memory/weak_ptr.cc",
     "memory/weak_ptr.h",
     "message_loop/incoming_task_queue.cc",
     "message_loop/incoming_task_queue.h",
@@ skipping 634 matching lines @@
       "files/file_util_proxy.cc",
       "files/important_file_writer.cc",
       "files/important_file_writer.h",
       "files/scoped_temp_dir.cc",
       "memory/discardable_memory.cc",
       "memory/discardable_memory.h",
       "memory/discardable_memory_allocator.cc",
       "memory/discardable_memory_allocator.h",
       "memory/discardable_shared_memory.cc",
       "memory/discardable_shared_memory.h",
+      "memory/shared_memory_helper.cc",
+      "memory/shared_memory_helper.h",
       "memory/shared_memory_posix.cc",
       "native_library.cc",
       "native_library_posix.cc",
       "path_service.cc",
       "process/kill.cc",
       "process/kill.h",
       "process/memory.cc",
       "process/memory.h",
       "process/process_iterator.cc",
       "process/process_iterator.h",
@@ skipping 1348 matching lines @@
 }
 
 fuzzer_test("base_json_correctness_fuzzer") {
   sources = [
     "json/correctness_fuzzer.cc",
   ]
   deps = [
     ":base",
   ]
 }