WIP (Introduce WTF::NonNullPtr<T>.)

Source/core/css/ElementRuleCollector.cpp

Index: Source/core/css/ElementRuleCollector.cpp
diff --git a/Source/core/css/ElementRuleCollector.cpp b/Source/core/css/ElementRuleCollector.cpp
index 5ccfc77f50439c5ac436b6bd0d9d8b06f8dc850c..2384ae2dc45fb22bdf890b5aa02db480ce1bf87e 100644
--- a/Source/core/css/ElementRuleCollector.cpp
+++ b/Source/core/css/ElementRuleCollector.cpp
@@ -100,14 +100,14 @@ void ElementRuleCollector::addElementStyleProperties(const StylePropertySet* pro
 
 static bool rulesApplicableInCurrentTreeScope(const Element* element, const ContainerNode* scopingNode, SelectorChecker::BehaviorAtBoundary behaviorAtBoundary, bool elementApplyAuthorStyles)
 {
-    TreeScope& treeScope = element->treeScope();
+    NonNullPtr<TreeScope> treeScope = element->treeScope();
 
     // [skipped, because already checked] a) it's a UA rule
     // b) element is allowed to apply author rules
     if (elementApplyAuthorStyles)
         return true;
     // c) the rules comes from a scoped style sheet within the same tree scope
-    if (!scopingNode || &treeScope == &scopingNode->treeScope())
+    if (!scopingNode || treeScope == scopingNode->treeScope())
         return true;
     // d) the rules comes from a scoped style sheet within an active shadow root whose host is the given element
     if (element->isInShadowTree() && (behaviorAtBoundary & SelectorChecker::ScopeIsShadowHost) && scopingNode == element->containingShadowRoot()->host())