Avoid WTF::Vector::at() and operator[] in core/dom.

third_party/WebKit/Source/core/dom/shadow/InsertionPoint.cpp

Index: third_party/WebKit/Source/core/dom/shadow/InsertionPoint.cpp
diff --git a/third_party/WebKit/Source/core/dom/shadow/InsertionPoint.cpp b/third_party/WebKit/Source/core/dom/shadow/InsertionPoint.cpp
index da2cae918d1a05759b8d286e9176479a5e5ef5e7..43ebb054c7cd7c8ee87ede7c0ac3102cf0340430 100644
--- a/third_party/WebKit/Source/core/dom/shadow/InsertionPoint.cpp
+++ b/third_party/WebKit/Source/core/dom/shadow/InsertionPoint.cpp
@@ -157,10 +157,7 @@ bool InsertionPoint::isActive() const {
 
   // Slow path only when there are more than one shadow elements in a shadow
   // tree. That should be a rare case.
-  const HeapVector<Member<InsertionPoint>>& insertionPoints =
-      shadowRoot->descendantInsertionPoints();
-  for (size_t i = 0; i < insertionPoints.size(); ++i) {
-    InsertionPoint* point = insertionPoints[i].get();
+  for (const auto& point : shadowRoot->descendantInsertionPoints()) {
     if (isHTMLShadowElement(*point))
       return point == this;
   }