Reland "Implement FullScreen using top layer."

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 0237c178a90d10d43bb4150ec865e83db8984ccb..b2e77da1059967583af8a7a403786243266a7d05 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -5302,9 +5302,12 @@ void Document::removeFromTopLayer(Element* element)
 
 HTMLDialogElement* Document::activeModalDialog() const
 {
-    if (m_topLayerElements.isEmpty())
-        return 0;
-    return toHTMLDialogElement(m_topLayerElements.last().get());
+    for (auto it = m_topLayerElements.rbegin(); it != m_topLayerElements.rend(); ++it) {
+        if (isHTMLDialogElement(*it))
+            return toHTMLDialogElement((*it).get());
+    }
+
+    return nullptr;
 }
 
 void Document::exitPointerLock()