Support slot element's fallback content feature

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/shadow/SlotAssignment.h"
 
 #include "core/HTMLNames.h"
 #include "core/dom/ElementTraversal.h"
 #include "core/dom/NodeTraversal.h"
 #include "core/dom/shadow/InsertionPoint.h"
@@ skipping 13 matching lines @@
         node.lazyReattachIfAttached();
 }
 
 void SlotAssignment::resolveAssignment(const ShadowRoot& shadowRoot)
 {
     m_assignment.clear();
 
     using Name2Slot = HashMap<AtomicString, HTMLSlotElement*>;
     Name2Slot name2slot;
     HTMLSlotElement* defaultSlot = nullptr;
+    Vector<HTMLSlotElement*> slots;
 
     // TODO(hayato): Cache slots elements so that we do not have to travese the shadow tree. See ShadowRoot::descendantInsertionPoints()
     for (HTMLSlotElement& slot : Traversal<HTMLSlotElement>::descendantsOf(shadowRoot)) {
         slot.clearDistribution();
 
+        slots.append(&slot);
+
         AtomicString name = slot.fastGetAttribute(HTMLNames::nameAttr);
         if (name.isNull() || name.isEmpty()) {
             if (!defaultSlot)
                 defaultSlot = &slot;
         } else {
             name2slot.add(name, &slot);
         }
     }
 
     for (Node& child : NodeTraversal::childrenOf(*shadowRoot.host())) {
@@ skipping 15 matching lines @@
                     assign(child, *slot);
                 else
                     detachNotAssignedNode(child);
             }
         } else if (defaultSlot) {
             assign(child, *defaultSlot);
         } else {
             detachNotAssignedNode(child);
         }
     }
+
+    // Update each slot's distribution in reverse tree order so that a child slot is visited before its parent slot.
+    for (auto slot = slots.rbegin(); slot != slots.rend(); ++slot)
+        (*slot)->updateDistributedNodesWithFallback();
 }
 
 void SlotAssignment::assign(Node& hostChild, HTMLSlotElement& slot)
 {
     m_assignment.add(&hostChild, &slot);
     slot.appendAssignedNode(hostChild);
     if (isHTMLSlotElement(hostChild))
         slot.appendDistributedNodes(toHTMLSlotElement(hostChild).getDistributedNodes());
     else
         slot.appendDistributedNode(hostChild);
 }
 
 DEFINE_TRACE(SlotAssignment)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_assignment);
 #endif
 }
 
 } // namespace blink