Add a queue for custom element reactions.

third_party/WebKit/Source/core/dom/custom/CustomElementReaction.h

Index: third_party/WebKit/Source/core/dom/custom/CustomElementReaction.h
diff --git a/third_party/WebKit/Source/core/dom/custom/CustomElementReaction.h b/third_party/WebKit/Source/core/dom/custom/CustomElementReaction.h
new file mode 100644
index 0000000000000000000000000000000000000000..3ee1ab254ab26a4bd846871539b9b1036ff03731
--- /dev/null
+++ b/third_party/WebKit/Source/core/dom/custom/CustomElementReaction.h
@@ -0,0 +1,28 @@
+// 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.
+
+#ifndef CustomElementReaction_h
+#define CustomElementReaction_h
+
+#include "core/CoreExport.h"
+#include "platform/heap/Handle.h"
+#include "wtf/Noncopyable.h"
+
+namespace blink {
+
+class Element;
+
+class CORE_EXPORT CustomElementReaction
+    : public GarbageCollectedFinalized<CustomElementReaction> {
+    WTF_MAKE_NONCOPYABLE(CustomElementReaction);
+public:
+    CustomElementReaction() { }

[yosin_UTC9, 2016/06/01 02:14:01]

nit: %s/{ }/ = default/

+    virtual ~CustomElementReaction() { }
+    DEFINE_INLINE_VIRTUAL_TRACE() { }
+    virtual void invoke(Element*) = 0;
+};
+
+} // namespace blink
+
+#endif // CustomElementReaction_h