Enable GN build on Mac.

build/toolchain/mac/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.
 
 # TODO(brettw) Use "gcc_toolchain.gni" like the Linux toolchains. This requires
 # some enhancements since the commands on Mac are slightly different than on
 # Linux.
 
 import("../goma.gni")
 import("//build/config/ios/ios_sdk.gni")
 import("//build/config/mac/mac_sdk.gni")
 
 assert(host_os == "mac")
 
 import("//build/toolchain/clang.gni")
 import("//build/toolchain/goma.gni")
 import("//build/config/sysroot.gni")
 
 if (use_goma) {
   goma_prefix = "$goma_dir/gomacc "
 } else {
   goma_prefix = ""
 }
 
 # This will copy the gyp-mac-tool to the build directory. We pass in the source
 # file of the win tool.
 gyp_mac_tool_source =
-    rebase_path("//tools/gyp/pylib/gyp/mac_tool.py", root_build_dir)
+    rebase_path("//third_party/gyp/pylib/gyp/mac_tool.py", root_build_dir)
 exec_script("setup_toolchain.py", [ gyp_mac_tool_source ])
 
 # Shared toolchain definition. Invocations should set toolchain_os to set the
 # build args in this definition.
 template("mac_toolchain") {
   toolchain(target_name) {
     assert(defined(invoker.cc), "mac_toolchain() must specify a \"cc\" value")
     assert(defined(invoker.cxx), "mac_toolchain() must specify a \"cxx\" value")
     assert(defined(invoker.ld), "mac_toolchain() must specify a \"ld\" value")
     assert(defined(invoker.toolchain_cpu),
@@ skipping 213 matching lines @@
   toolchain_cpu = "i386"
   toolchain_os = "mac"
   prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                        root_build_dir)
   cc = "${goma_prefix}$prefix/clang"
   cxx = "${goma_prefix}$prefix/clang++"
   ld = cxx
   is_clang = true
   sysroot_flags = "-isysroot $mac_sdk_path -mmacosx-version-min=$mac_sdk_min"
 }