Upgrade in-document custom elements when an element is defined.

third_party/WebKit/Source/core/dom/custom/CEReactionsScope.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.
+
+#ifndef CEReactionsScope_h
+#define CEReactionsScope_h
+
+#include "core/CoreExport.h"
+#include "platform/heap/Handle.h"
+#include "wtf/Allocator.h"
+#include "wtf/Noncopyable.h"
+#include "wtf/StdLibExtras.h"
+
+namespace blink {
+
+class CustomElementReaction;
+class Element;
+class FrameHost;
+
+// https://html.spec.whatwg.org/multipage/scripting.html#cereactions
+class CORE_EXPORT CEReactionsScope final {
+    STACK_ALLOCATED();
+    WTF_MAKE_NONCOPYABLE(CEReactionsScope);
+public:
+    static CEReactionsScope* current()

[yosin_UTC9, 2016/06/02 07:16:02]

So, you think this class is performance critical and it is worth to expose
implementation, s_topOfStack, detail in .h file.
My preference is all of them in .cpp file and make s_topOfStack is file static
variable instead of static class member.
Anyway, this is personal preference and performance consideration.

+    {
+        return s_topOfStack;
+    }
+
+    CEReactionsScope()
+        : m_prev(s_topOfStack)
+    {
+        s_topOfStack = this;
+    }
+
+    ~CEReactionsScope()
+    {
+        s_topOfStack = s_topOfStack->m_prev;
+        if (m_frameHost.get())
+            invokeReactions();
+    }
+
+    void enqueue(Element*, CustomElementReaction*);
+
+private:
+    static CEReactionsScope* s_topOfStack;
+
+    void invokeReactions();
+
+    CEReactionsScope* m_prev;
+    Member<FrameHost> m_frameHost;
+};
+
+} // namespace blink
+
+#endif // CEReactionsScope_h