Support serializing shadow DOM to MHTML

third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.cpp

Index: third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.cpp
diff --git a/third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.cpp b/third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.cpp
index c8cbc31e60ee0f9f49c624b8beffe41dbaff43cf..d922cd9465c801a70270c1326de75375c00c07a7 100644
--- a/third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.cpp
+++ b/third_party/WebKit/Source/core/editing/serializers/MarkupAccumulator.cpp
@@ -151,6 +151,12 @@ bool MarkupAccumulator::SerializeAsHTMLDocument(const Node& node) const {
   return formatter_.SerializeAsHTMLDocument(node);
 }
 
+Node* MarkupAccumulator::GetAuxiliaryDOMTree(
+    const Element& element,
+    Element** enclosing_element) const {
+  return nullptr;
+}
+
 template <typename Strategy>
 static void SerializeNodesWithNamespaces(MarkupAccumulator& accumulator,
                                          Node& target_node,
@@ -177,6 +183,24 @@ static void SerializeNodesWithNamespaces(MarkupAccumulator& accumulator,
     for (; current; current = Strategy::NextSibling(*current))
       SerializeNodesWithNamespaces<Strategy>(accumulator, *current,
                                              kIncludeNode, &namespace_hash);
+
+    // Traverses other DOM tree, i.e., shadow tree.
+    if (target_node.IsElementNode()) {
+      Element* enclosing_element = nullptr;
+      Node* auxiliary_tree = accumulator.GetAuxiliaryDOMTree(
+          ToElement(target_node), &enclosing_element);
+      if (auxiliary_tree) {
+        if (enclosing_element)
+          accumulator.AppendStartTag(*enclosing_element);
+        current = Strategy::FirstChild(*auxiliary_tree);
+        for (; current; current = Strategy::NextSibling(*current)) {
+          SerializeNodesWithNamespaces<Strategy>(accumulator, *current,
+                                                 kIncludeNode, &namespace_hash);
+        }
+        if (enclosing_element)
+          accumulator.AppendEndTag(*enclosing_element);
+      }
+    }
   }
 
   if ((!children_only && target_node.IsElementNode()) &&