Implement custom element construction and some 'define' checks

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 AtomicString& localName,
+    v8::Isolate* isolate,
+    v8::Handle<v8::Object> prototype)
+    : m_localName(localName)
+    , m_prototype(isolate, prototype)
+{
+    m_prototype.setWeak(this, &CustomElementDefinition::didCollectPrototype);
+}
+
+v8::Local<v8::Object> CustomElementDefinition::prototype(
+    v8::Isolate* isolate) const
+{
+    v8::Local<v8::Object> object = m_prototype.newLocal(isolate);
+    DCHECK(!object.IsEmpty());

[haraken, 2016/05/10 09:04:22]

Would you help me understand who guarantees that m_prototype is not empty?
m_prototype is a weak persistent handle, which may be cleared at any point.

[dominicc (has gone to gerrit), 2016/05/11 02:31:49]

CustomElementsRegistry::visitDOMWrapper ends up calling
CustomElementDefinition::setReference and keeping the prototype alive. That
should be enough?

+    return object;
+}
+
+void CustomElementDefinition::didCollectPrototype(
+    const v8::WeakCallbackInfo<CustomElementDefinition>& info)
+{
+    info.GetParameter()->m_prototype.clear();
+}
+
+} // namespace blink