Get content_unittests to link on the mac GN build.

content/common/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/config/features.gni")
 import("//build/config/ui.gni")
 import("//content/common/common.gni")
 import("//third_party/mojo/src/mojo/public/tools/bindings/mojom.gni")
+if (is_mac) {
+  import("//build/config/mac/mac_sdk.gni")
+}
 
 if (is_chromeos && current_cpu != "arm") {
   action("libva_generate_stubs") {
     extra_header = "gpu/media/va_stub_header.fragment"
 
     script = "../../tools/generate_stubs/generate_stubs.py"
     sources = [
       "gpu/media/va.sigs",
     ]
     inputs = [
@@ skipping 202 matching lines @@
     sources -= [ "plugin_list_posix.cc" ]
 
     deps += [
       ":libvt_generate_stubs",
       "//content/app/resources",
       "//content:resources",
       "//third_party/WebKit/public:image_resources",
       "//third_party/WebKit/public:resources",
       "//ui/accelerated_widget_mac",
     ]
+    lib_dirs = [ "$mac_sdk_path/usr/lib" ]
     libs += [
       "IOSurface.framework",
       "OpenGL.framework",
       "QuartzCore.framework",
+      "sandbox",
     ]
   }
 
   if (is_android) {
     sources += [
       "gpu/client/gpu_memory_buffer_impl_surface_texture.cc",
       "gpu/client/gpu_memory_buffer_impl_surface_texture.h",
       "gpu/gpu_memory_buffer_factory_surface_texture.cc",
       "gpu/gpu_memory_buffer_factory_surface_texture.h",
     ]
@@ skipping 260 matching lines @@
 
   import_dirs = [ "//mojo/services" ]
 
   deps = [
     "//content/public/common:mojo_bindings",
     "//mojo/application/public/interfaces",
     "//skia/public/interfaces",
     "//ui/mojo/geometry:interfaces",
   ]
 }