DOM: Remove standard-violating optimizations in appendChild, insertBefore, and replaceChild.

third_party/WebKit/Source/core/dom/ContainerNode.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2013 Apple Inc. All rights
  * reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 248 matching lines @@
  public:
   inline void operator()(ContainerNode& container, Node& child, Node*) const {
     container.treeScope().adoptIfNeeded(child);
     container.appendChildCommon(child);
   }
 };
 
 Node* ContainerNode::insertBefore(Node* newChild,
                                   Node* refChild,
                                   ExceptionState& exceptionState) {
+  // https://dom.spec.whatwg.org/#concept-node-pre-insert
+
   // insertBefore(node, 0) is equivalent to appendChild(node)
   if (!refChild)
     return appendChild(newChild, exceptionState);
 
   // Make sure adding the new child is OK.
   if (!checkAcceptChild(newChild, 0, exceptionState))
     return newChild;
   DCHECK(newChild);
 
   // NotFoundError: Raised if refChild is not a child of this node
   if (refChild->parentNode() != this) {
     exceptionState.throwDOMException(NotFoundError,
                                      "The node before which the new node is to "
                                      "be inserted is not a child of this "
                                      "node.");
     return nullptr;
   }
 
-  // Nothing to do.
-  if (refChild->previousSibling() == newChild || refChild == newChild)
-    return newChild;
+  // 3. If reference child is node, set it to node’s next sibling.
+  if (refChild == newChild) {
+    refChild = newChild->nextSibling();
+    if (!refChild)
+      return appendChild(newChild, exceptionState);
+  }
 
   NodeVector targets;
   if (!collectChildrenAndRemoveFromOldParentWithCheck(
           refChild, nullptr, *newChild, targets, exceptionState))
     return newChild;
 
   ChildListMutationScope mutation(*this);
   insertNodeVector(targets, refChild, AdoptAndInsertBefore());
   return newChild;
 }
@@ skipping 84 matching lines @@
     DCHECK_EQ(newChild->connectedSubframeCount(), 0u);
     ChildListMutationScope(*this).childAdded(*newChild);
   }
 
   notifyNodeInserted(*newChild, ChildrenChangeSourceParser);
 }
 
 Node* ContainerNode::replaceChild(Node* newChild,
                                   Node* oldChild,
                                   ExceptionState& exceptionState) {
-  if (oldChild == newChild)  // Nothing to do.
-    return oldChild;
+  // https://dom.spec.whatwg.org/#concept-node-replace
 
   if (!oldChild) {
     exceptionState.throwDOMException(NotFoundError,
                                      "The node to be replaced is null.");
     return nullptr;
   }
 
   // Make sure replacing the old child with the new is OK.
   if (!checkAcceptChild(newChild, oldChild, exceptionState))
     return oldChild;
 
   // NotFoundError: Raised if oldChild is not a child of this node.
   if (oldChild->parentNode() != this) {
     exceptionState.throwDOMException(
         NotFoundError, "The node to be replaced is not a child of this node.");
     return nullptr;
   }
 
   ChildListMutationScope mutation(*this);
+  // 7. Let reference child be child’s next sibling.
   Node* next = oldChild->nextSibling();
+  // 8. If reference child is node, set it to node’s next sibling.
+  if (next == newChild)
+    next = newChild->nextSibling();
 
-  // Remove the node we're replacing.
+  // TODO(tkent): According to the specification, we should remove |newChild|
+  // from its parent here, and create a separated mutation record for it.
+  // Refer to imported/wpt/dom/nodes/MutationObserver-childList.html.
+
+  // 12. If child’s parent is not null, run these substeps:
+  //    1. Set removedNodes to a list solely containing child.
+  //    2. Remove child from its parent with the suppress observers flag set.
   removeChild(oldChild, exceptionState);
   if (exceptionState.hadException())
     return nullptr;
 
-  if (next && (next->previousSibling() == newChild ||
-               next == newChild))  // nothing to do
-    return oldChild;
-
   // Does this one more time because removeChild() fires a MutationEvent.
   if (!checkAcceptChild(newChild, oldChild, exceptionState))
     return oldChild;
 
   NodeVector targets;
   if (!collectChildrenAndRemoveFromOldParentWithCheck(next, oldChild, *newChild,
                                                       targets, exceptionState))
     return oldChild;
 
   if (next)
@@ skipping 206 matching lines @@
     dispatchSubtreeModifiedEvent();
 }
 
 Node* ContainerNode::appendChild(Node* newChild,
                                  ExceptionState& exceptionState) {
   // Make sure adding the new child is ok
   if (!checkAcceptChild(newChild, 0, exceptionState))
     return newChild;
   DCHECK(newChild);
 
-  if (newChild == m_lastChild)  // nothing to do
-    return newChild;
-
   NodeVector targets;
   if (!collectChildrenAndRemoveFromOldParentWithCheck(
           nullptr, nullptr, *newChild, targets, exceptionState))
     return newChild;
 
   ChildListMutationScope mutation(*this);
   insertNodeVector(targets, nullptr, AdoptAndAppendChild());
   return newChild;
 }
 
@@ skipping 805 matching lines @@
     return true;
 
   if (node->isElementNode() && toElement(node)->shadow())
     return true;
 
   return false;
 }
 #endif
 
 }  // namespace blink