Hook up allocator shim on mac.

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index c370c214a61d93d8427aacd57ef8e4ce3250a0fa..ef37887da467505a0e31565e7211e651faef01eb 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -1146,6 +1146,12 @@ component("base") {
         "allocator/allocator_shim_override_linker_wrapped_symbols.h",
       ]
       all_dependent_configs += [ "//base/allocator:wrap_malloc_symbols" ]
+    } else if (is_mac) {
+      sources += [
+        "allocator/allocator_shim_default_dispatch_to_mac_zoned_malloc.cc",
+        "allocator/allocator_shim_default_dispatch_to_mac_zoned_malloc.h",
+        "allocator/allocator_shim_override_mac_symbols.h",
+      ]
     }
   }