Remove support for custom pseudo elements.

Source/core/css/SelectorChecker.cpp

Index: Source/core/css/SelectorChecker.cpp
diff --git a/Source/core/css/SelectorChecker.cpp b/Source/core/css/SelectorChecker.cpp
index 855288f27b3bb2622d5f0032bb7aeb1b0aae84c2..1af455ad71392b0434244e98cfafaa3bc64f4473 100644
--- a/Source/core/css/SelectorChecker.cpp
+++ b/Source/core/css/SelectorChecker.cpp
@@ -68,12 +68,11 @@ SelectorChecker::SelectorChecker(Document& document, Mode mode)
 static bool matchesCustomPseudoElement(const Element* element, const CSSSelector& selector)
 {
     ShadowRoot* root = element->containingShadowRoot();
-    if (!root)
+    if (!root || root->type() != ShadowRoot::UserAgentShadowRoot)
         return false;
+
     if (element->shadowPseudoId() != selector.value())
         return false;
-    if (selector.pseudoType() == CSSSelector::PseudoWebKitCustomElement && root->type() != ShadowRoot::UserAgentShadowRoot)
-        return false;
 
     return true;
 }