Support slotchange event

third_party/WebKit/Source/core/dom/shadow/ElementShadow.cpp

Index: third_party/WebKit/Source/core/dom/shadow/ElementShadow.cpp
diff --git a/third_party/WebKit/Source/core/dom/shadow/ElementShadow.cpp b/third_party/WebKit/Source/core/dom/shadow/ElementShadow.cpp
index aa11696e48e513f271c11440900cbd4e7b20a427..3ec5ffdba9003c54ff332adab1ec6d32a8b21cef 100644
--- a/third_party/WebKit/Source/core/dom/shadow/ElementShadow.cpp
+++ b/third_party/WebKit/Source/core/dom/shadow/ElementShadow.cpp
@@ -30,6 +30,7 @@
 #include "core/dom/ElementTraversal.h"
 #include "core/dom/NodeTraversal.h"
 #include "core/dom/StyleChangeReason.h"
+#include "core/dom/StyleEngine.h"
 #include "core/dom/shadow/DistributedNodes.h"
 #include "core/frame/Deprecation.h"
 #include "core/html/HTMLContentElement.h"
@@ -170,6 +171,8 @@ ShadowRoot& ElementShadow::addShadowRoot(Element& shadowHost, ShadowRootType typ
     shadowRoot->setParentTreeScope(shadowHost.treeScope());
     m_shadowRoots.push(shadowRoot);
     setNeedsDistributionRecalc();
+    if (shadowHost.document().shadowCascadeOrder() == ShadowCascadeOrder::ShadowCascadeV1)
+        shadowHost.document().updateAssignment();
 
     shadowRoot->insertedInto(&shadowHost);
     shadowHost.setChildNeedsStyleRecalc();
@@ -348,6 +351,8 @@ void ElementShadow::willAffectSelector()
         shadow->setNeedsSelectFeatureSet();
     }
     setNeedsDistributionRecalc();
+    if (host()->document().shadowCascadeOrder() == ShadowCascadeOrder::ShadowCascadeV1)
+        host()->document().updateAssignment();
 }
 
 void ElementShadow::clearDistribution()