Implement :defined pseudo-class selector for Custom Elements

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

Index: third_party/WebKit/Source/core/dom/Node.cpp
diff --git a/third_party/WebKit/Source/core/dom/Node.cpp b/third_party/WebKit/Source/core/dom/Node.cpp
index b6a7a56d31ed645f6b99c6b0f2a1318f155af947..3454897bbc798c792c8c4960ef9d20cc233b2b15 100644
--- a/third_party/WebKit/Source/core/dom/Node.cpp
+++ b/third_party/WebKit/Source/core/dom/Node.cpp
@@ -2341,15 +2341,21 @@ void Node::setCustomElementState(CustomElementState newState)
 
     DCHECK(isHTMLElement());
     DCHECK_NE(V0Upgraded, getV0CustomElementState());
+#if DCHECK_IS_ON()
+    bool wasDefined = toElement(this)->isDefined();
+#endif
 
     setFlag(CustomElementFlag);
     if (newState == CustomElementState::Custom)
         setFlag(CustomElementCustomFlag);
     DCHECK(newState == getCustomElementState());
 
-    // TODO(kojii): Should fire pseudoStateChanged() when :defined selector is
-    // ready.
-    // toElement(this)->pseudoStateChanged(CSSSelector::PseudoDefined);
+    // When the state goes from Uncustomized to Undefined, and then to Custom,
+    // isDefined is always flipped.
+#if DCHECK_IS_ON()
+    DCHECK_NE(wasDefined, toElement(this)->isDefined());
+#endif
+    toElement(this)->pseudoStateChanged(CSSSelector::PseudoDefined);
 }
 
 void Node::setV0CustomElementState(V0CustomElementState newState)