Extend LargeIconService to fetch missing favicons from a Google server

components/favicon/core/features.h

Index: components/favicon/core/features.h
diff --git a/components/favicon/core/features.h b/components/favicon/core/features.h
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+// 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_FAVICON_CORE_FEATURES_H_
+#define COMPONENTS_FAVICON_CORE_FEATURES_H_
+
+#include "base/feature_list.h"
+
+namespace favicon {
+
+// Features to turn on Google backend servers to fetch large icons on demand.
+extern const base::Feature kFaviconFetchLargeIconFromGoogleServer1;
+extern const base::Feature kFaviconFetchLargeIconFromGoogleServer2;
+
+}  // namespace favicon
+
+#endif  // COMPONENTS_FAVICON_CORE_FEATURES_H_