Reland of Fix FlatTreeTraversal for a slot in a document tree

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

Index: third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversalTest.cpp
diff --git a/third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversalTest.cpp b/third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversalTest.cpp
index 9a760954036120eaae760c73b22b2ff1e0cde479..b3056b82b15e7562a0646974a1f878fb91ab17c0 100644
--- a/third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversalTest.cpp
+++ b/third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversalTest.cpp
@@ -571,4 +571,26 @@
   EXPECT_EQ(nullptr, FlatTreeTraversal::parent(*d4));
 }
 
+TEST_F(FlatTreeTraversalTest, v1SlotInDocumentTree) {
+  const char* mainHTML =
+      "<div id='parent'>"
+      "<slot>"
+      "<div id='child1'></div>"
+      "<div id='child2'></div>"
+      "</slot>"
+      "</div>";
+
+  setupDocumentTree(mainHTML);
+  Element* body = document().body();
+  Element* parent = body->querySelector("#parent");
+  Element* child1 = body->querySelector("#child1");
+  Element* child2 = body->querySelector("#child2");
+
+  EXPECT_EQ(child1, FlatTreeTraversal::firstChild(*parent));
+  EXPECT_EQ(child2, FlatTreeTraversal::nextSibling(*child1));
+  EXPECT_EQ(nullptr, FlatTreeTraversal::nextSibling(*child2));
+  EXPECT_EQ(parent, FlatTreeTraversal::parent(*child1));
+  EXPECT_EQ(parent, FlatTreeTraversal::parent(*child2));
+}
+
 }  // namespace blink