Mark gtest and gmock as testonly in GN.

sql/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.
 
 component("sql") {
   sources = [
     "connection.cc",
     "connection.h",
     "error_delegate_util.cc",
     "error_delegate_util.h",
@@ skipping 15 matching lines @@
   }
 
   deps = [
     "//base",
     "//third_party/sqlite",
     "//base/third_party/dynamic_annotations",
   ]
 }
 
 source_set("test_support") {
+  testonly = true
   sources = [
     "test/error_callback_support.cc",
     "test/error_callback_support.h",
     "test/scoped_error_ignorer.cc",
     "test/scoped_error_ignorer.h",
     "test/test_helpers.cc",
     "test/test_helpers.h",
   ]
 
   deps = [
@@ skipping 44 matching lines @@
   #'target_name': 'sql_unittests_apk',
   #'type': 'none',
   #'dependencies': [
   #  'sql_unittests',
   #],
   #'variables': {
   #  'test_suite_name': 'sql_unittests',
   #},
   #'includes': [ '../build/apk_test.gypi' ],
 }