WTF/std normalization: replace WTF::Vector::last with ::back

third_party/WebKit/Source/core/dom/ElementVisibilityObserver.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/ElementVisibilityObserver.h"
 
 #include "core/dom/Element.h"
 #include "core/dom/IntersectionObserverEntry.h"
 #include "core/frame/LocalFrame.h"
 #include "wtf/Functional.h"
@@ skipping 56 matching lines @@
   m_intersectionObserver->deliver();
 }
 
 DEFINE_TRACE(ElementVisibilityObserver) {
   visitor->trace(m_element);
   visitor->trace(m_intersectionObserver);
 }
 
 void ElementVisibilityObserver::onVisibilityChanged(
     const HeapVector<Member<IntersectionObserverEntry>>& entries) {
-  bool isVisible = entries.last()->intersectionRatio() > 0.f;
+  bool isVisible = entries.back()->intersectionRatio() > 0.f;
   (*m_callback.get())(isVisible);
 }
 
 }  // namespace blink