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

third_party/WebKit/Source/core/html/track/vtt/VTTParser.cpp

Index: third_party/WebKit/Source/core/html/track/vtt/VTTParser.cpp
diff --git a/third_party/WebKit/Source/core/html/track/vtt/VTTParser.cpp b/third_party/WebKit/Source/core/html/track/vtt/VTTParser.cpp
index ba84d045921b26c8ab927ba6880d279e31fe6a43..54e1fb8fd8848e0dd460a5de5ad8536c2efe3fe6 100644
--- a/third_party/WebKit/Source/core/html/track/vtt/VTTParser.cpp
+++ b/third_party/WebKit/Source/core/html/track/vtt/VTTParser.cpp
@@ -524,10 +524,10 @@ void VTTTreeBuilder::constructTreeFromToken(Document& document) {
       } else if (nodeType == VTTNodeTypeLanguage) {
         m_languageStack.append(m_token.annotation());
         child->setAttribute(VTTElement::langAttributeName(),
-                            m_languageStack.last());
+                            m_languageStack.back());
       }
       if (!m_languageStack.isEmpty())
-        child->setLanguage(m_languageStack.last());
+        child->setLanguage(m_languageStack.back());
       m_currentNode->parserAppendChild(child);
       m_currentNode = child;
       break;