make base::SharedMemoryHandle a class on POSIX.

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 1088 matching lines @@
       "base_paths_posix.h",
       "base_paths_win.cc",
       "base_paths_win.h",
     ]
 
     if (is_linux) {
       sources += [ "base_paths_posix.cc" ]
     }
   }
 
+  if (!is_mac && is_posix) {
+    sources += [ "memory/shared_memory_handle_posix.cc" ]
+  }
+
   all_dependent_configs = []
   defines = []
   data = []
 
   configs += [
     ":base_flags",
     ":base_implementation",
     "//base/allocator:allocator_shim_define",  # for allocator_check.cc.
     "//build/config:precompiled_headers",
   ]
@@ skipping 1575 matching lines @@
 }
 
 fuzzer_test("base_json_correctness_fuzzer") {
   sources = [
     "json/correctness_fuzzer.cc",
   ]
   deps = [
     ":base",
   ]
 }