Mark gtest and gmock as testonly in GN.

components/policy/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("//third_party/protobuf/proto_library.gni")
 import("//tools/grit/grit_rule.gni")
 
 if (is_component_build) {
   component("policy_component") {
@@ skipping 120 matching lines @@
   }
 
   group("test_support") {
     deps = [
       ":chrome_settings_proto_generated_compile",
       ":policy",
     ]
   }
 
   static_library("policy_component_test_support") {
+    testonly = true
     sources = [
       "core/browser/configuration_policy_pref_store_test.cc",
       "core/browser/configuration_policy_pref_store_test.h",
       "core/common/cloud/mock_cloud_external_data_manager.cc",
       "core/common/cloud/mock_cloud_external_data_manager.h",
       "core/common/cloud/mock_cloud_policy_client.cc",
       "core/common/cloud/mock_cloud_policy_client.h",
       "core/common/cloud/mock_cloud_policy_store.cc",
       "core/common/cloud/mock_cloud_policy_store.h",
       "core/common/cloud/mock_device_management_service.cc",
@@ skipping 25 matching lines @@
       ":policy_component",
       ":test_support",
       "//components/policy/proto",
       "//testing/gmock",
       "//testing/gtest",
     ]
   }
 }
 
 #TODO(GYP) policy templates, chrome_manifest_bundle