Move enable extensions define to a build flag.

google_apis/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("//extensions/features/features.gni")
 import("//testing/test.gni")
 
 declare_args() {
   # You can set the variable 'use_official_google_api_keys' to true
   # to use the Google-internal file containing official API keys
   # for Google Chrome even in a developer build.  Setting this
   # variable explicitly to true will cause your build to fail if the
   # internal file is missing.
   #
   # The variable is documented here, but not handled in this file;
@@ skipping 258 matching lines @@
   }
 
   if (is_mac || is_ios) {
     set_sources_assignment_filter([])
     sources += [ "google_api_keys_mac_unittest.mm" ]
     set_sources_assignment_filter(sources_assignment_filter)
 
     deps += [ "//third_party/ocmock" ]
   }
 }