Make --headless flag work on Mac

chrome/BUILD.gn

 # Copyright 2014 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/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/compiler/pgo/pgo.gni")
 import("//build/config/features.gni")
 import("//build/config/locales.gni")
@@ skipping 961 matching lines @@
     ]
 
     deps = [
       ":browser_dependencies",
       ":child_dependencies",
       "//chrome/app:command_ids",
       "//chrome/common:features",
       "//components/crash/content/app",
       "//components/policy:generated",
       "//content/public/app:both",
+      "//headless:headless_shell_lib",
       "//pdf",
       "//third_party/cld",
     ]
 
     if (is_component_build) {
       libs = [ "Carbon.framework" ]
     }
 
     ldflags = [
       "-Wl,-order_file",
@@ skipping 624 matching lines @@
       "//chrome/app/theme/$branding_path_component/product_logo_48.png",
       "//chrome/tools/build/linux/chrome-wrapper",
       "//third_party/xdg-utils/scripts/xdg-mime",
       "//third_party/xdg-utils/scripts/xdg-settings",
     ]
     outputs = [
       "$root_out_dir/{{source_file_part}}",
     ]
   }
 }