Styling slot fallback content with ::slotted()

third_party/WebKit/Source/core/css/SelectorChecker.cpp

Index: third_party/WebKit/Source/core/css/SelectorChecker.cpp
diff --git a/third_party/WebKit/Source/core/css/SelectorChecker.cpp b/third_party/WebKit/Source/core/css/SelectorChecker.cpp
index 86a68368667e7ce6e0f9daff6d0c8b93e0a910f4..f32020804c7b50187b81f898a62c182a6a152c64 100644
--- a/third_party/WebKit/Source/core/css/SelectorChecker.cpp
+++ b/third_party/WebKit/Source/core/css/SelectorChecker.cpp
@@ -123,8 +123,12 @@ static const HTMLSlotElement* FindSlotElementInScope(
   if (!context.scope)
     return context.element->AssignedSlot();
 
-  for (const HTMLSlotElement* slot = context.element->AssignedSlot(); slot;
-       slot = slot->AssignedSlot()) {
+  const HTMLSlotElement* slot = context.element->AssignedSlot();
+  if (!slot)
+    slot = HTMLSlotElement::FindFallbackSlotElementFor(*context.element);
+
+  // Find the slot element that matches the scope.
+  for (; slot; slot = slot->AssignedSlot()) {
     if (slot->GetTreeScope() == context.scope->GetTreeScope())
       return slot;
   }