Begin to enable extension APIs in Extension Service Worker.

extensions/common/features/feature_util.cc

+// Copyright 2016 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.
+
+#include "extensions/common/features/feature_util.h"
+
+namespace extensions {
+namespace feature_util {
+
+namespace {
+
+bool g_extension_api_enabled_in_extension_service_workers = false;
+
+}  // namespace
+
+bool ExtensionAPIEnabledInExtensionServiceWorkers() {
+  return g_extension_api_enabled_in_extension_service_workers;
+}
+
+void SetExtensionAPIEnabledInExtensionServiceWorkers(bool enabled) {
+  g_extension_api_enabled_in_extension_service_workers = enabled;
+}
+
+}  // namespace feature_util
+}  // namespace extensions