Mark gtest and gmock as testonly in GN.

components/autofill/core/browser/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.
 
 if (is_android) {
   import("//build/config/android/config.gni")
   autofill_enable_sync = !is_android_webview_build
 } else {
   autofill_enable_sync = true
 }
@@ skipping 156 matching lines @@
     ]
   }
 
   if (is_win) {
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     cflags = [ "/wd4267" ]
   }
 }
 
 static_library("test_support") {
+  testonly = true
   sources = [
     "autofill_test_utils.cc",
     "autofill_test_utils.h",
     "data_driven_test.cc",
     "data_driven_test.h",
     "test_autofill_client.cc",
     "test_autofill_client.h",
     "test_autofill_driver.cc",
     "test_autofill_driver.h",
     "test_autofill_external_delegate.cc",
     "test_autofill_external_delegate.h",
     "test_personal_data_manager.cc",
     "test_personal_data_manager.h",
   ]
 
   deps = [
     ":browser",
     "//components/autofill/core/browser",
     "//components/autofill/core/common",
     "//skia",
     "//testing/gtest",
   ]
 }
 
 source_set("unit_tests") {
+  testonly = true
   sources = [
     "address_field_unittest.cc",
     "address_unittest.cc",
     "autocomplete_history_manager_unittest.cc",
     "autofill_country_unittest.cc",
     "autofill_data_model_unittest.cc",
     "autofill_download_manager_unittest.cc",
     "autofill_external_delegate_unittest.cc",
     "autofill_field_unittest.cc",
     "autofill_ie_toolbar_import_win_unittest.cc",
@@ skipping 24 matching lines @@
   deps = [
     ":browser",
     ":test_support",
     "//components/resources",
     "//components/strings",
     "//testing/gmock",
     "//third_party/libphonenumber",
     "//third_party/libjingle"
   ]
 }