Support slotchange event

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

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index fe8f945943988dc2dfd501ec228d51f66d6d92c7..1a5accb21ff73fceb930953ceea1b22bb6fe2b1a 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -1140,8 +1140,10 @@ void Element::attributeChanged(const QualifiedName& name, const AtomicString& ol
         if (shouldInvalidateDistributionWhenAttributeChanged(parentElementShadow, name, newValue))
             parentElementShadow->setNeedsDistributionRecalc();
     }
-    if (name == HTMLNames::slotAttr && isChildOfV1ShadowHost())
+    if (name == HTMLNames::slotAttr && isChildOfV1ShadowHost()) {
         parentElementShadow()->setNeedsDistributionRecalc();
+        document().updateAssignment();
+    }
 
     parseAttribute(name, oldValue, newValue);
 
@@ -2069,8 +2071,13 @@ void Element::childrenChanged(const ChildrenChange& change)
     if (!change.byParser && change.isChildElementChange())
         checkForSiblingStyleChanges(change.type == ElementRemoved ? SiblingElementRemoved : SiblingElementInserted, change.siblingBeforeChange, change.siblingAfterChange);
 
-    if (ElementShadow* shadow = this->shadow())
+    if (ElementShadow* shadow = this->shadow()) {
         shadow->setNeedsDistributionRecalc();
+        if (document().shadowCascadeOrder() == ShadowCascadeOrder::ShadowCascadeV1) {
+            if ((isShadowHost(*this) && shadowRoot()->isV1()) || isHTMLSlotElement(*this))
+                document().updateAssignment();
+        }
+    }
 }
 
 void Element::finishParsingChildren()