Add Ignition to about:flags.

gin/public/gin_features.h

+// 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.
+
+// This file defines all the public base::FeatureList features for the gin
+// module.
+
+#ifndef GIN_PUBLIC_GIN_FEATURES_H_
+#define GIN_PUBLIC_GIN_FEATURES_H_
+
+#include "base/feature_list.h"
+#include "gin/gin_export.h"
+
+namespace features {
+
+GIN_EXPORT extern const base::Feature kV8Ignition;
+
+}  // namespace features
+
+#endif  // GIN_PUBLIC_GIN_FEATURES_H_