[Extensions Bindings] Add ChromeSetting custom type

extensions/renderer/api_custom_types.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 EXTENSIONS_RENDERER_API_CUSTOM_TYPES_H_
+#define EXTENSIONS_RENDERER_API_CUSTOM_TYPES_H_
+
+#include "base/strings/string_piece.h"
+
+namespace extensions {
+class APISignature;
+
+namespace api_custom_types {
+
+// Returns the schema associated with the specified function.
+const APISignature& GetFunctionSchema(base::StringPiece api_name,
+                                      base::StringPiece type_name,
+                                      base::StringPiece function_name);
+
+}  // namespace api_custom_types
+}  // namespace extensions
+
+#endif  // EXTENSIONS_RENDERER_API_CUSTOM_TYPES_H_