Get content_unittests to link on the mac GN build.

printing/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("//testing/test.gni")
 if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
 }
@@ skipping 217 matching lines @@
     "//ui/gfx:test_support",
     "//ui/gfx/geometry",
   ]
 }
 
 if (use_cups) {
   config("cups") {
     defines = [ "USE_CUPS" ]
 
     if (is_mac) {
-      ldflags = [ "$mac_sdk_path/usr/lib/libcups.dylib" ]
+      libs = [ "cups" ]
+      lib_dirs = [ "$mac_sdk_path/usr/lib" ]
     } else {
       libs = exec_script("cups_config_helper.py", [ "--libs-for-gn" ], "value")
     }
   }
 }
 
 if (is_android) {
   # GYP: //printing/printing.gyp:printing_jni_headers
   generate_jni("printing_jni_headers") {
     sources = [
       "android/java/src/org/chromium/printing/PrintingContext.java",
     ]
     jni_package = "printing"
   }
 
   # GYP: //printing/printing.gyp:printing_java
   android_library("printing_java") {
     deps = [
       "//base:base_java",
     ]
     DEPRECATED_java_in_dir = "android/java/src"
   }
 }