Adding an Android about:flags feature for offline previews

components/previews/core/previews_features.h

+// Copyright 2017 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.
+
+#ifndef COMPONENTS_PREVIEWS_CORE_PREVIEWS_FEATURES_H_
+#define COMPONENTS_PREVIEWS_CORE_PREVIEWS_FEATURES_H_
+
+#include "base/feature_list.h"
+
+namespace previews {
+namespace features {
+
+extern const base::Feature kOfflinePreviews;
+
+}  // namespace features
+}  // namespace previews
+
+#endif  // COMPONENTS_PREVIEWS_CORE_PREVIEWS_FEATURES_H_