Support slot element's fallback content feature

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

Index: third_party/WebKit/Source/core/html/HTMLSlotElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLSlotElement.h b/third_party/WebKit/Source/core/html/HTMLSlotElement.h
index 66d3eba312322ce15ed7bcb3bf08c15e0040a76c..a6e1ba9d0f3d4217cc3c8ce3666b13b83eb5f41e 100644
--- a/third_party/WebKit/Source/core/html/HTMLSlotElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLSlotElement.h
@@ -42,7 +42,6 @@ public:
     DECLARE_NODE_FACTORY(HTMLSlotElement);
 
     const WillBeHeapVector<RefPtrWillBeMember<Node>> getAssignedNodes() const { return m_assignedNodes; }
-    // TODO(hayato): Support fallback contents of slot elements
     const WillBeHeapVector<RefPtrWillBeMember<Node>> getDistributedNodes() const { return m_distributedNodes; }
 
     Node* firstDistributedNode() const { return m_distributedNodes.isEmpty() ? nullptr : m_distributedNodes.first().get(); }
@@ -57,6 +56,8 @@ public:
     void appendDistributedNodes(const WillBeHeapVector<RefPtrWillBeMember<Node>>&);
     void clearDistribution();
 
+    void updateDistributedNodesWithFallback();
+
     void attach(const AttachContext& = AttachContext()) override;
     void detach(const AttachContext& = AttachContext()) override;