Introduce Node::containingTreeScope(), which asserts that the node's root is a tree scope

third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp

Index: third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp b/third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp
index 44e1ea74218499dabb8e715c3678410fa3cc8817..91db0389652ef8b4fedd38d1aaec5242e303ec90 100644
--- a/third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/StyleResolver.cpp
@@ -512,15 +512,15 @@ void StyleResolver::matchScopedRules(const Element& element, ElementRuleCollecto
     bool matchElementScopeDone = !elementScopeResolver && !element.inlineStyle();
 
     for (auto it = m_treeBoundaryCrossingScopes.rbegin(); it != m_treeBoundaryCrossingScopes.rend(); ++it) {
-        const TreeScope& scope = (*it)->treeScope();
+        const TreeScope& scope = (*it)->rootTreeScope();
         ScopedStyleResolver* resolver = scope.scopedStyleResolver();
         ASSERT(resolver);
 
-        bool isInnerTreeScope = element.treeScope().isInclusiveAncestorOf(scope);
+        bool isInnerTreeScope = element.rootTreeScope().isInclusiveAncestorOf(scope);
         if (!shouldCheckScope(element, **it, isInnerTreeScope))
             continue;
 
-        if (!matchElementScopeDone && scope.isInclusiveAncestorOf(element.treeScope())) {
+        if (!matchElementScopeDone && scope.isInclusiveAncestorOf(element.rootTreeScope())) {
 
             matchElementScopeDone = true;
 
@@ -660,7 +660,7 @@ void StyleResolver::collectTreeBoundaryCrossingRules(const Element& element, Ele
     for (const auto& scopingNode : m_treeBoundaryCrossingScopes) {
         // Skip rule collection for element when tree boundary crossing rules of scopingNode's
         // scope can never apply to it.
-        bool isInnerTreeScope = element.treeScope().isInclusiveAncestorOf(scopingNode->treeScope());
+        bool isInnerTreeScope = element.rootTreeScope().isInclusiveAncestorOf(scopingNode->rootTreeScope());
         if (!shouldCheckScope(element, *scopingNode, isInnerTreeScope))
             continue;