[css-display] Support display: contents pseudo-elements.

third_party/WebKit/Source/core/layout/LayoutObject.cpp

Index: third_party/WebKit/Source/core/layout/LayoutObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.cpp b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
index 6e66dcecbf1827f0aa76ed281430a9a10e05164a..c5a185e1fde853ee40e84ddfb8704a3eebe5bf01 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -174,8 +174,11 @@ LayoutObject* LayoutObject::createObject(Element* element,
 
   switch (style.display()) {
     case EDisplay::None:
-    case EDisplay::Contents:
       return nullptr;
+    case EDisplay::Contents:
+      if (LIKELY(!element->isPseudoElement()))
+        return nullptr;
+    // fall through
     case EDisplay::Inline:
       return new LayoutInline(element);
     case EDisplay::Block:
@@ -3019,6 +3022,9 @@ ComputedStyle* LayoutObject::cachedFirstLineStyle() const {
 ComputedStyle* LayoutObject::getCachedPseudoStyle(
     PseudoId pseudo,
     const ComputedStyle* parentStyle) const {
+  DCHECK_NE(pseudo, PseudoIdBefore);
+  DCHECK_NE(pseudo, PseudoIdAfter);
+
   if (pseudo < FirstInternalPseudoId && !style()->hasPseudoStyle(pseudo))
     return nullptr;