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

third_party/WebKit/Source/core/events/TreeScopeEventContext.cpp

 /*
  * Copyright (C) 2014 Google 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 94 matching lines @@
 }
 
 int TreeScopeEventContext::calculateTreeOrderAndSetNearestAncestorClosedTree(
     int orderNumber,
     TreeScopeEventContext* nearestAncestorClosedTreeScopeEventContext) {
   m_preOrder = orderNumber;
   m_containingClosedShadowTree =
       (rootNode().isShadowRoot() && !toShadowRoot(rootNode()).isOpenOrV0())
           ? this
           : nearestAncestorClosedTreeScopeEventContext;
-  for (size_t i = 0; i < m_children.size(); ++i)
-    orderNumber =
-        m_children[i]->calculateTreeOrderAndSetNearestAncestorClosedTree(
-            orderNumber + 1, containingClosedShadowTree());
+  for (const auto& context : m_children) {
+    orderNumber = context->calculateTreeOrderAndSetNearestAncestorClosedTree(
+        orderNumber + 1, containingClosedShadowTree());
+  }
   m_postOrder = orderNumber + 1;
 
   return orderNumber + 1;
 }
 
 }  // namespace blink