Add backup element queue to CustomElementReactionStack

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

Index: third_party/WebKit/Source/core/dom/custom/CEReactionsScope.h
diff --git a/third_party/WebKit/Source/core/dom/custom/CEReactionsScope.h b/third_party/WebKit/Source/core/dom/custom/CEReactionsScope.h
index 8b9f2967a18a3d40e148eb9ca9b4396f6c03ca79..b9280828cd58097829ce36bc3d5f1020f8d490f7 100644
--- a/third_party/WebKit/Source/core/dom/custom/CEReactionsScope.h
+++ b/third_party/WebKit/Source/core/dom/custom/CEReactionsScope.h
@@ -14,6 +14,7 @@
 namespace blink {
 
 class CustomElementReaction;
+class CustomElementReactionStack;
 class Element;
 class FrameHost;
 
@@ -22,11 +23,6 @@ class CORE_EXPORT CEReactionsScope final {
     STACK_ALLOCATED();
     WTF_MAKE_NONCOPYABLE(CEReactionsScope);
 public:
-    static CEReactionsScope* current()
-    {
-        return s_topOfStack;
-    }
-
     CEReactionsScope()
         : m_prev(s_topOfStack)
     {
@@ -40,7 +36,8 @@ public:
         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;