Handle fallback content case in FlatTreeTraversal::traverseSiblings()

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

Index: third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversal.cpp
diff --git a/third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversal.cpp b/third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversal.cpp
index 8e498b52afc88b645c2629d9c170bf420a0405c4..43254c76eeba006d7f8f85783784ad91a22bb4e0 100644
--- a/third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversal.cpp
+++ b/third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversal.cpp
@@ -134,6 +134,18 @@ Node* FlatTreeTraversal::traverseSiblings(const Node& node,
           direction))
     return found;
 
+  if (node.isInV1ShadowTree()) {

[hayato, 2017/03/16 09:32:56]

Instead of this early check, could you use slot.suppportDistribution() to judge
the slot is *active* or not?
It is more consistent, and more robust for a future change.

[kochi, 2017/03/16 10:09:54]

Done.
Actually it looks better now.  Thanks for the suggestion.

+    // Slotted nodes are already handled in traverseSiblingsForV1HostChild()
+    // above, here is for fallback contents.
+    Element* parent = node.parentElement();
+    if (parent && isHTMLSlotElement(parent)) {
+      HTMLSlotElement& slot = toHTMLSlotElement(*parent);
+      if (!slot.assignedNodes().isEmpty())
+        return nullptr;
+      return traverseSiblings(slot, direction);
+    }
+  }
+
   if (!node.isInV0ShadowTree())
     return nullptr;