Reland "Implement FullScreen using top layer."

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

Index: third_party/WebKit/Source/core/dom/PseudoElement.cpp
diff --git a/third_party/WebKit/Source/core/dom/PseudoElement.cpp b/third_party/WebKit/Source/core/dom/PseudoElement.cpp
index 1672b8600b09a7c432d66599f8dce9bbf0f2a27a..424e89ef1ae320566eedb4c4c705890a6fa2b75a 100644
--- a/third_party/WebKit/Source/core/dom/PseudoElement.cpp
+++ b/third_party/WebKit/Source/core/dom/PseudoElement.cpp
@@ -29,6 +29,7 @@
 #include "core/dom/FirstLetterPseudoElement.h"
 #include "core/frame/UseCounter.h"
 #include "core/inspector/InspectorInstrumentation.h"
+#include "core/layout/GeneratedChildren.h"
 #include "core/layout/LayoutObject.h"
 #include "core/layout/LayoutQuote.h"
 #include "core/style/ContentData.h"
@@ -124,6 +125,13 @@ void PseudoElement::attach(const AttachContext& context)
     if (!layoutObject)
         return;
 
+    // This is to ensure that bypassing the canHaveGeneratedChildren check in
+    // StyleResolver::createPseudoElementIfNeeded does not result in the
+    // backdrop pseudo element's layout object becoming the child of a layout
+    // object that doesn't allow children.
+    DCHECK(layoutObject->parent());
+    DCHECK(canHaveGeneratedChildren(*layoutObject->parent()));
+
     ComputedStyle& style = layoutObject->mutableStyleRef();
     if (style.styleType() != PseudoIdBefore && style.styleType() != PseudoIdAfter)
         return;