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

third_party/WebKit/Source/core/dom/custom/CustomElementDefinition.cpp

 // 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.
 
 #include "core/dom/custom/CustomElementDefinition.h"
 
 namespace blink {
 
 CustomElementDefinition::CustomElementDefinition(
     const CustomElementDescriptor& descriptor)
     : m_descriptor(descriptor)
 {
 }
 
 CustomElementDefinition::~CustomElementDefinition()
 {
 }
 
+DEFINE_TRACE(CustomElementDefinition)
+{
+    visitor->trace(m_constructionStack);
+}
+
+// https://html.spec.whatwg.org/multipage/scripting.html#concept-upgrade-an-element
+void CustomElementDefinition::upgrade(Element* element)
+{
+    size_t depth = m_constructionStack.size();
+    m_constructionStack.append(element);
+
+    bool succeeded = runConstructor(element);
+
+    // Pop the construction stack.
+    if (m_constructionStack.last().get())
+        DCHECK_EQ(m_constructionStack.last(), element);
+    m_constructionStack.removeLast();
+    DCHECK_EQ(m_constructionStack.size(), depth); // It's a *stack*.

[yosin_UTC9, 2016/06/02 04:06:38]

Better way to catch weird situation is:

m_constructionStack.append(element);
size_t depth = m_constructionStack.size();
bool succeeded = runConstructor(element);
DCHECK_EQ(m_constructionStack.size(), depth);

Above sequence tells compiler that removing |RELEASE_ASSERT(index < size.())| in
|at()| via |last()| is safe.

+
+    if (!succeeded)
+        return;
+
+    // TODO(dominicc): Turn this into an assertion when setting
+    // 'custom' moves to the HTMLElement constructor. We will need to
+    // add a bit for MARQUEE to be custom-gets-callbacks-yet-not-custom.
+    element->setCustomElementState(CustomElementState::Custom);
+
+    // TODO(dominicc): When the attributeChangedCallback is implemented,
+    // enqueue reactions for attributes here.
+    // TODO(dominicc): When the connectedCallback is implemented, enqueue
+    // reactions here, if applicable.
+}
+
+bool CustomElementDefinition::runConstructor(Element*)
+{
+    return true;
+}
+
 } // namespace blink