Mark gtest and gmock as testonly in GN.

components/component_updater/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.
 
 source_set("component_updater") {
   sources = [
     "background_downloader_win.cc",
     "background_downloader_win.h",
     "component_patcher.cc",
     "component_patcher.h",
@@ skipping 34 matching lines @@
     "//courgette:courgette_lib",
     "//crypto",
     "//third_party/libxml",
     "//third_party/zlib:zip",
     "//net",
     "//ui/base",
   ]
 }
 
 static_library("test_support") {
+  testonly = true
   sources = [
     "test/test_configurator.cc",
     "test/test_configurator.h",
     "test/test_installer.cc",
     "test/test_installer.h",
     "test/url_request_post_interceptor.cc",
     "test/url_request_post_interceptor.h",
   ]
 
   deps = [
     ":component_updater",
     "//testing/gtest",
     "//testing/gmock",
   ]
 }
 
 source_set("unit_tests") {
+  testonly = true
   sources = [
     "test/component_patcher_unittest.cc",
     "test/component_updater_ping_manager_unittest.cc",
     "test/crx_downloader_unittest.cc",
     "test/update_checker_unittest.cc",
     "test/update_response_unittest.cc",
   ]
 
   deps = [
     ":component_updater",
     ":test_support",
     "//testing/gtest",
     "//testing/gmock",
     "//third_party/libxml",
   ]
 }