[WIP] Migrate Fullscreen to use top layer instead of RenderFullScreen

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 27207a8de35eb20383e80ee5c5b0ce87fc6efed2..1569f4a58adb51987d25bcadd5babf58924b4e30 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -429,6 +429,7 @@ Document::Document(const DocumentInit& initializer, DocumentClassFlags documentC
     , m_weakFactory(this)
     , m_contextDocument(initializer.contextDocument())
     , m_hasFullscreenElementStack(false)
+    , m_activeModalDialog(0)
     , m_loadEventDelayCount(0)
     , m_loadEventDelayTimer(this, &Document::loadEventDelayTimerFired)
     , m_referrerPolicy(ReferrerPolicyDefault)
@@ -4722,9 +4723,9 @@ void Document::addToTopLayer(Element* element, const Element* before)
 {
     if (element->isInTopLayer())
         return;
-
     ASSERT(!m_topLayerElements.contains(element));
     ASSERT(!before || m_topLayerElements.contains(before));
+
     if (before) {
         size_t beforePosition = m_topLayerElements.find(before);
         m_topLayerElements.insert(beforePosition, element);
@@ -4744,11 +4745,41 @@ void Document::removeFromTopLayer(Element* element)
     element->setIsInTopLayer(false);
 }
 
+void Document::addToModalDialogStack(HTMLDialogElement* dialog)
+{
+    if (dialog->isModal())
+        return;
+    addToTopLayer(dialog);
+    dialog->setModal(true);
+    m_activeModalDialog = dialog;
+}
+
+void Document::removeFromModalDialogStack(HTMLDialogElement* dialog)
+{
+    if (!dialog->isModal())
+        return;
+
+    removeFromTopLayer(dialog);
+    dialog->setModal(false);
+    if (m_activeModalDialog != dialog)
+        return;
+
+    m_activeModalDialog = 0;
+    Vector<RefPtr<Element> >::reverse_iterator end = m_topLayerElements.rend();
+    for (Vector<RefPtr<Element> >::reverse_iterator it = m_topLayerElements.rbegin(); it != end; ++it) {
+        if (!it->get()->hasTagName(dialogTag))
+            continue;
+        HTMLDialogElement* dialog = toHTMLDialogElement(it->get());
+        if (dialog->isModal()) {
+            m_activeModalDialog = dialog;
+            return;
+        }
+    }
+}
+
 HTMLDialogElement* Document::activeModalDialog() const
 {
-    if (m_topLayerElements.isEmpty())
-        return 0;
-    return toHTMLDialogElement(m_topLayerElements.last().get());
+    return m_activeModalDialog;
 }
 
 void Document::webkitExitPointerLock()