Revert r174436 (Reduce the cost of the n^2 loop in collectTreeBoundaryCrossingRules)

Source/core/css/TreeBoundaryCrossingRules.cpp

Index: Source/core/css/TreeBoundaryCrossingRules.cpp
diff --git a/Source/core/css/TreeBoundaryCrossingRules.cpp b/Source/core/css/TreeBoundaryCrossingRules.cpp
index e45aa3f8d1546a1beb9e5b3603d14e9dbfd2c914..503eb839a9988fed48b940fa82369c9ba1b8dc06 100644
--- a/Source/core/css/TreeBoundaryCrossingRules.cpp
+++ b/Source/core/css/TreeBoundaryCrossingRules.cpp
@@ -32,7 +32,6 @@
 #include "core/css/ElementRuleCollector.h"
 #include "core/css/RuleFeature.h"
 #include "core/dom/StyleEngine.h"
-#include "core/dom/shadow/InsertionPoint.h"
 #include "core/dom/shadow/ShadowRoot.h"
 
 namespace WebCore {
@@ -74,8 +73,6 @@ void TreeBoundaryCrossingRules::collectTreeBoundaryCrossingRules(Element* elemen
     // When comparing rules declared in inner treescopes, inner's rules win.
     CascadeOrder innerCascadeOrder = size();
 
-    // FIXME: This is n^2 across the number of scoping nodes in the entire document! We need to walk the
-    // ancestors of |element| instead.
     for (DocumentOrderedList::iterator it = m_scopingNodes.begin(); it != m_scopingNodes.end(); ++it) {
         const ContainerNode* scopingNode = toContainerNode(*it);
         CSSStyleSheetRuleSubSet* ruleSubSet = m_treeBoundaryCrossingRuleSetMap.get(scopingNode);
@@ -89,24 +86,12 @@ void TreeBoundaryCrossingRules::collectTreeBoundaryCrossingRules(Element* elemen
             scopingNode = toShadowRoot(scopingNode)->host();
         }
 
-        // FIXME: This is a terrible hack to avoid doing most of the work in this n^2 loop.
-        // Instead we should just fix the loop to collect the proper scopes up the tree instead
-        // of iterating all possible scopes.
-        const InsertionPoint* insertionPoint = resolveReprojection(element);
-        if ((insertionPoint && !scopingNode->containsIncludingShadowDOM(insertionPoint))
-            || (!insertionPoint && !scopingNode->containsIncludingShadowDOM(element))) {
-            ++innerCascadeOrder;
-            --outerCascadeOrder;
-            continue;
-        }
-
         CascadeOrder cascadeOrder = isInnerTreeScope ? innerCascadeOrder : outerCascadeOrder;
         for (CSSStyleSheetRuleSubSet::iterator it = ruleSubSet->begin(); it != ruleSubSet->end(); ++it) {
             CSSStyleSheet* parentStyleSheet = it->first;
             RuleSet* ruleSet = it->second.get();
             collector.collectMatchingRules(MatchRequest(ruleSet, includeEmptyRules, scopingNode, parentStyleSheet), ruleRange, static_cast<SelectorChecker::BehaviorAtBoundary>(boundaryBehavior), ignoreCascadeScope, cascadeOrder);
         }
-
         ++innerCascadeOrder;
         --outerCascadeOrder;
     }