mac: Hook up allocator shim.

base/allocator/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.
 
 import("//build/buildflag_header.gni")
 import("//build/config/allocator.gni")
 import("//build/config/compiler/compiler.gni")
 
 declare_args() {
   # Provide a way to force disable debugallocation in Debug builds,
@@ skipping 326 matching lines @@
         ":tcmalloc",
       ]
     } else if (is_linux && use_allocator == "none") {
       sources += [ "allocator_shim_default_dispatch_to_glibc.cc" ]
     } else if (is_android && use_allocator == "none") {
       sources += [
         "allocator_shim_default_dispatch_to_linker_wrapped_symbols.cc",
         "allocator_shim_override_linker_wrapped_symbols.h",
       ]
       all_dependent_configs = [ ":wrap_malloc_symbols" ]
+    } else if (is_mac) {
+      sources += [ "allocator_shim_override_mac_symbols.h" ]
     }
   }
 }