Support slot element's fallback content feature

third_party/WebKit/Source/core/html/HTMLSlotElement.cpp

 /*
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "core/html/HTMLSlotElement.h"
 
 #include "core/HTMLNames.h"
+#include "core/dom/NodeTraversal.h"
+#include "core/dom/shadow/InsertionPoint.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
 inline HTMLSlotElement::HTMLSlotElement(Document& document)
     : HTMLElement(slotTag, document)
 {
 }
 
@@ skipping 47 matching lines @@
 }
 
 void HTMLSlotElement::detach(const AttachContext& context)
 {
     for (auto& node : m_distributedNodes)
         node->lazyReattachIfAttached();
 
     HTMLElement::detach(context);
 }
 
+void HTMLSlotElement::updateDistributedNodesWithFallback()
+{
+    if (!m_distributedNodes.isEmpty())
+        return;
+    for (auto& child : NodeTraversal::childrenOf(*this)) {
+        // Insertion points are not supported as slots fallback
+        if (isActiveInsertionPoint(child))
+            continue;
+        if (isHTMLSlotElement(child))
+            appendDistributedNodes(toHTMLSlotElement(child).getDistributedNodes());
+        else
+            appendDistributedNode(child);
+    }
+}
+
 DEFINE_TRACE(HTMLSlotElement)
 {
     visitor->trace(m_assignedNodes);
     visitor->trace(m_distributedNodes);
     HTMLElement::trace(visitor);
 }
 
 }