Fix assignedNodes({flatten:true}) to return fallback content in document tree

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

Index: third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp b/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
index e0edd169f36c12e64323efbbc0a80edeaf7b26ee..cf08b7963980a811f61b1929372886e52b3d4cd3 100644
--- a/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
@@ -79,7 +79,11 @@ HTMLSlotElement::GetDistributedNodesForBinding() {
   DCHECK(!NeedsDistributionRecalc());
   if (SupportsDistribution())
     return distributed_nodes_;
+  return GetDistributedNodesOfSlotInDocument();
+}
 
+const HeapVector<Member<Node>>
+HTMLSlotElement::GetDistributedNodesOfSlotInDocument() const {
   // If a slot does not support distribution, its m_distributedNodes should not
   // be used.  Instead, calculate distribution manually here. This happens only
   // in a slot in non-shadow trees, so its assigned nodes are always empty.
@@ -132,7 +136,14 @@ void HTMLSlotElement::AppendDistributedNode(Node& node) {
 
 void HTMLSlotElement::AppendDistributedNodesFrom(const HTMLSlotElement& other) {
   size_t index = distributed_nodes_.size();
-  distributed_nodes_.AppendVector(other.distributed_nodes_);
+
+  if (other.SupportsDistribution()) {

[hayato, 2017/05/12 03:19:09]

Could you avoid if else here?
It looks a functional duplication of GetDistributedNodesForBinding.

[kochi, 2017/05/12 07:26:33]

I see, having inconsistent distributed_nodes_ and distributed_indices_
would be also problematic.  Let me work on it.

[kochi, 2017/05/12 07:53:14]

Hmm, this function is called when resolving distribution, to have
a cached distributed nodes in |distributed_nodes_|.

|distributed_nodes_| of slots in non-shadow tree are still empty.

If we don't calculate |distributed_nodes_| for slots in shadow
tree here, GetDistributedNodesForBinding() has to go though all
|distributed_nodes_| to see if there is any slot that contains
fallback content in it, and insert manually calculated distributed
nodes. This will make assignedNodes({flatten:true}) slower.

GetDistributedNodesForBinding() does manual calculation if |this|
is a slot in non-shadow tree.  So I don't think this is duplicate.

+    distributed_nodes_.AppendVector(other.distributed_nodes_);
+  } else {
+    distributed_nodes_.AppendVector(
+        other.GetDistributedNodesOfSlotInDocument());
+  }
+
   for (const auto& node : other.distributed_nodes_)
     distributed_indices_.Set(node.Get(), index++);
 }