Get rid of TreeBoundaryCrossingRules.

Source/core/dom/TreeScope.cpp

 /*
  * Copyright (C) 2011 Google Inc. All Rights Reserved.
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 42 matching lines @@
 #include "wtf/Vector.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
 TreeScope::TreeScope(ContainerNode& rootNode, Document& document)
     : m_rootNode(&rootNode)
     , m_document(&document)
     , m_parentTreeScope(&document)
+    , m_composedParent(nullptr)
 #if !ENABLE(OILPAN)
     , m_guardRefCount(0)
 #endif
     , m_idTargetObserverRegistry(IdTargetObserverRegistry::create())
 {
     ASSERT(rootNode != document);
 #if !ENABLE(OILPAN)
     m_parentTreeScope->guardRef();
 #endif
     m_rootNode->setTreeScope(this);
@@ skipping 488 matching lines @@
 {
     for (Element* element = ElementTraversal::firstWithin(rootNode()); element; element = ElementTraversal::nextIncludingPseudo(*element)) {
         for (ShadowRoot* root = element->youngestShadowRoot(); root; root = root->olderShadowRoot())
             root->setNeedsStyleRecalcForViewportUnits();
         const ComputedStyle* style = element->computedStyle();
         if (style && style->hasViewportUnits())
             element->setNeedsStyleRecalc(LocalStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::ViewportUnits));
     }
 }
 
+TreeScope* TreeScope::composedParent()
+{
+    if (rootNode().isDocumentNode())
+        return nullptr;
+    if (!m_composedParent) {
+        ShadowRoot& root = toShadowRoot(rootNode());
+        if (root.olderShadowRoot())
+            m_composedParent = root.olderShadowRoot();
+        else if (ContainerNode* host = rootNode().parentOrShadowHostNode())
+            m_composedParent = treeScopeInComposedTree(*host);

[esprehn, 2015/05/19 02:37:56]

Can we update these pointers inside the updateDistribution phase instead? I'd
rather that and make the getter inline and do no branching.

[rune, 2015/05/19 11:08:18]

Maybe, I need to look closer at the distribution code. We probably do update
distribution in tree-of-trees order which possibly makes it more costly, as we
would need to traverse down the composed tree finding the tree-scopes that needs
composedParent updates. Also, we might not want to update composedParent
pointers in display:none subtrees (we don't know the display type at
distribution time), yet we need to find the composedParent if we query for
computed style inside a display:none sub-tree. So, there are various concerns
here, and I don't have the full overview yet.

+    }
+    return m_composedParent;
+}
+
+TreeScope* TreeScope::treeScopeInComposedTree(const Node& node)
+{
+    for (Node* composedParent = ComposedTreeTraversal::parent(node); composedParent; composedParent = ComposedTreeTraversal::parent(*composedParent)) {
+        if (composedParent && isShadowHost(composedParent))

[esprehn, 2015/05/19 02:37:56]

This null check doesn't make sense, you're in a loop that already checked it

[rune, 2015/05/19 11:08:18]

Done.

+            return toElement(composedParent)->shadow()->youngestShadowRoot();

[esprehn, 2015/05/19 02:37:56]

there's a getter right on Node for this, just do
composedParent->youngestShadowRoot().

[rune, 2015/05/19 11:08:18]

Done.

+    }
+    return &node.document();
+}
+
 DEFINE_TRACE(TreeScope)
 {
     visitor->trace(m_rootNode);
     visitor->trace(m_document);
     visitor->trace(m_parentTreeScope);
+    visitor->trace(m_composedParent);
     visitor->trace(m_idTargetObserverRegistry);
     visitor->trace(m_selection);
     visitor->trace(m_elementsById);
     visitor->trace(m_imageMapsByName);
     visitor->trace(m_labelsByForAttribute);
     visitor->trace(m_scopedStyleResolver);
 }
 
 } // namespace blink