Add backup element queue to CustomElementReactionStack

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 CustomElementReactionStack;
 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()
-    {
-        return s_topOfStack;
-    }
-
     CEReactionsScope()
         : m_prev(s_topOfStack)
     {
         s_topOfStack = this;
     }
 
     ~CEReactionsScope()
     {
         if (m_frameHost.get())
             invokeReactions();
         s_topOfStack = s_topOfStack->m_prev;
     }
 
-    void enqueue(Element*, CustomElementReaction*);
+    static CustomElementReactionStack* currentCustomElementReactionStack(

[dominicc (has gone to gerrit), 2016/06/28 03:37:13]

I think it would be better if we were not exposing the queues directly.

There needs to be coordination between the queues and the CEReactionsScope. The
CEReactionsScope should be cheap; it can't push and pop the reaction stack
eagerly. But it needs a bit set on it if it needs to pop the stack.

What about CustomElement::enqueue(Element*, CustomElementReaction*)? Then we can
limit the visibility of CustomElementReactionStack to within core/dom/custom.
Maybe CustomElement can do the coordination with CEReactionsScope so the
CustomElementReactionStack is easy to unit test; or it could make sense to have
CustomElementReactionStack mark the CEReactionsScope to ensure they stay in
sync. Up to you. As long is it happens in exactly one place.

FWIW Custom Elements v0 did this a bit differently. It was a bit subtle but kept
the reaction stack and scope a bit better separated. Let me know if you want
details.

[kojii, 2016/06/28 04:19:04]

Sounds good, done.

+        Element*);
 
 private:
     static CEReactionsScope* s_topOfStack;
 
     void invokeReactions();
 
     CEReactionsScope* m_prev;
     Member<FrameHost> m_frameHost;
 };
 
 } // namespace blink
 
 #endif // CEReactionsScope_h