Styling slot fallback content with ::slotted()

third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc.
  * All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
@@ skipping 249 matching lines @@
       resolver->CollectMatchingShadowHostRules(collector);
       collector.SortAndTransferMatchedRules();
       collector.FinishAddingAuthorRulesForTreeScope();
     }
   }
 }
 
 static void MatchSlottedRules(const Element& element,
                               ElementRuleCollector& collector) {
   HTMLSlotElement* slot = element.AssignedSlot();
-  if (!slot)
-    return;
+  if (!slot) {
+    slot = HTMLSlotElement::FindFallbackSlotElementFor(element);
+    if (!slot)
+      return;
+  }
 
   HeapVector<Member<ScopedStyleResolver>> resolvers;
   for (; slot; slot = slot->AssignedSlot()) {
     if (ScopedStyleResolver* resolver =
             slot->GetTreeScope().GetScopedStyleResolver())
       resolvers.push_back(resolver);
   }
   for (auto it = resolvers.rbegin(); it != resolvers.rend(); ++it) {
     collector.ClearMatchedRules();
     (*it)->CollectMatchingTreeBoundaryCrossingRules(collector);
@@ skipping 1735 matching lines @@
 
 DEFINE_TRACE(StyleResolver) {
   visitor->Trace(matched_properties_cache_);
   visitor->Trace(selector_filter_);
   visitor->Trace(style_sharing_lists_);
   visitor->Trace(document_);
   visitor->Trace(tracker_);
 }
 
 }  // namespace blink