CSS: Checked downcast for ShadowTreeStyleSheetCollection

third_party/WebKit/Source/core/dom/ShadowTreeStyleSheetCollection.h

Index: third_party/WebKit/Source/core/dom/ShadowTreeStyleSheetCollection.h
diff --git a/third_party/WebKit/Source/core/dom/ShadowTreeStyleSheetCollection.h b/third_party/WebKit/Source/core/dom/ShadowTreeStyleSheetCollection.h
index b74d6ccc98e7ece5e65d018cf1dbac7db185b101..a94cd34d8882c3fa1213cee6b8534dbc9929ef5f 100644
--- a/third_party/WebKit/Source/core/dom/ShadowTreeStyleSheetCollection.h
+++ b/third_party/WebKit/Source/core/dom/ShadowTreeStyleSheetCollection.h
@@ -43,6 +43,8 @@ public:
 
     void updateActiveStyleSheets(StyleEngine&, StyleResolverUpdateMode);
 
+    bool isShadowTreeStyleSheetCollection() const final { return true; }
+
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
         TreeScopeStyleSheetCollection::trace(visitor);
@@ -52,6 +54,8 @@ private:
     void collectStyleSheets(StyleEngine&, StyleSheetCollection&);
 };
 
+DEFINE_TYPE_CASTS(ShadowTreeStyleSheetCollection, TreeScopeStyleSheetCollection, value, value->isShadowTreeStyleSheetCollection(), value.isShadowTreeStyleSheetCollection());
+
 } // namespace blink
 
 #endif