Implement the ::backdrop pseudo-element for modal <dialog>.

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index 921392e15075276481840f28c6b872207fe33766..4b5c6a42e665e6e1295f3313561481a43994f9aa 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -205,6 +205,11 @@ Element::~Element()
         ElementRareData* data = elementRareData();
         data->setPseudoElement(BEFORE, 0);
         data->setPseudoElement(AFTER, 0);
+
+        if (Element* backdrop = data->pseudoElement(BACKDROP))
+            document()->removeFromTopLayer(backdrop);

[esprehn, 2013/07/04 08:34:07]

Lets just do this inside releasePseudoElement(). It seems fine to blindly call
element->document()->removeFromTopLayer(element) there since it's a noop if
they're not in the top layer anyway.

[falken, 2013/07/04 12:18:01]

Done.

+        data->setPseudoElement(BACKDROP, 0);
+
         data->clearShadow();
     }
 
@@ -1292,7 +1297,10 @@ void Element::removedFrom(ContainerNode* insertionPoint)
     if (Element* after = pseudoElement(AFTER))
         after->removedFrom(insertionPoint);
 
+    if (Element* backdrop = pseudoElement(BACKDROP))
+        backdrop->removedFrom(insertionPoint);
     document()->removeFromTopLayer(this);
+
     if (containsFullScreenElement())
         setContainsFullScreenElementOnAncestorsCrossingFrameBoundaries(false);
 
@@ -1350,6 +1358,7 @@ void Element::attach(const AttachContext& context)
     ContainerNode::attach(context);
 
     createPseudoElementIfNeeded(AFTER);
+    createPseudoElementIfNeeded(BACKDROP);
 
     if (hasRareData()) {
         ElementRareData* data = elementRareData();
@@ -1382,6 +1391,11 @@ void Element::detach(const AttachContext& context)
         ElementRareData* data = elementRareData();
         data->setPseudoElement(BEFORE, 0);
         data->setPseudoElement(AFTER, 0);
+
+        if (Element* backdrop = data->pseudoElement(BACKDROP))
+            document()->removeFromTopLayer(backdrop);

[esprehn, 2013/07/04 08:34:07]

Yeah lets do this in releasePseudoElement, then you don't need all the
duplication.

[falken, 2013/07/04 12:18:01]

Done.

+        data->setPseudoElement(BACKDROP, 0);
+
         data->setIsInCanvasSubtree(false);
         data->resetComputedStyle();
         data->resetDynamicRestyleObservations();
@@ -2415,15 +2429,21 @@ void Element::updatePseudoElement(PseudoId pseudoId, StyleChange change)
         // is false, otherwise we could continously create and destroy PseudoElements
         // when RenderObject::isChildAllowed on our parent returns false for the
         // PseudoElement's renderer for each style recalc.
-        if (!renderer() || !pseudoElementRendererIsNeeded(renderer()->getCachedPseudoStyle(pseudoId)))
+        if (!renderer() || !pseudoElementRendererIsNeeded(renderer()->getCachedPseudoStyle(pseudoId))) {
+            if (pseudoId == BACKDROP)
+                document()->removeFromTopLayer(element);

[esprehn, 2013/07/04 08:34:07]

Remove.

[falken, 2013/07/04 12:18:01]

Done.

             elementRareData()->setPseudoElement(pseudoId, 0);
+        }
     } else if (change >= Inherit || needsStyleRecalc())
         createPseudoElementIfNeeded(pseudoId);
 }
 
 void Element::createPseudoElementIfNeeded(PseudoId pseudoId)
 {
-    if (!document()->styleSheetCollection()->usesBeforeAfterRules())
+    if ((pseudoId == BEFORE || pseudoId == AFTER) && !document()->styleSheetCollection()->usesBeforeAfterRules())
+        return;
+
+    if (pseudoId == BACKDROP && !isInTopLayer())
         return;
 
     if (!renderer() || !pseudoElementRendererIsNeeded(renderer()->getCachedPseudoStyle(pseudoId)))
@@ -2436,6 +2456,9 @@ void Element::createPseudoElementIfNeeded(PseudoId pseudoId)
     RefPtr<PseudoElement> element = PseudoElement::create(this, pseudoId);
     element->attach();
     ensureElementRareData()->setPseudoElement(pseudoId, element.release());
+
+    if (pseudoId == BACKDROP)
+        document()->addToTopLayer(pseudoElement(BACKDROP), this);
 }
 
 PseudoElement* Element::pseudoElement(PseudoId pseudoId) const