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

third_party/WebKit/Source/core/dom/shadow/ElementShadowV0.cpp

Index: third_party/WebKit/Source/core/dom/shadow/ElementShadowV0.cpp
diff --git a/third_party/WebKit/Source/core/dom/shadow/ElementShadowV0.cpp b/third_party/WebKit/Source/core/dom/shadow/ElementShadowV0.cpp
index 5436c15968ee0bc48c2a0257d8c39ddc09b60ff3..28d5fdab329e5bc0cb7aeca110d0588ad0a28996 100644
--- a/third_party/WebKit/Source/core/dom/shadow/ElementShadowV0.cpp
+++ b/third_party/WebKit/Source/core/dom/shadow/ElementShadowV0.cpp
@@ -164,10 +164,7 @@ void ElementShadowV0::distribute() {
   for (ShadowRoot* root = &youngestShadowRoot(); root;
        root = root->olderShadowRoot()) {
     HTMLShadowElement* shadowInsertionPoint = 0;
-    const HeapVector<Member<InsertionPoint>>& insertionPoints =
-        root->descendantInsertionPoints();
-    for (size_t i = 0; i < insertionPoints.size(); ++i) {
-      InsertionPoint* point = insertionPoints[i];
+    for (const auto& point : root->descendantInsertionPoints()) {
       if (!point->isActive())
         continue;
       if (isHTMLShadowElement(*point)) {