GN: //base should not depend on //base/allocator on mac

We don't use tcmalloc or the allocator target on OS X

Review URL: https://codereview.chromium.org/311953002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274797 0039d316-1c4b-4281-b951-d872f2087c98

build/config/allocator.gni

@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-if (is_android || cpu_arch == "mipsel") {
+if (is_android || cpu_arch == "mipsel" || is_mac) {
   _default_allocator = "none"
 } else {
   _default_allocator = "tcmalloc"