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

third_party/WebKit/Source/core/html/track/TextTrackCueList.cpp

Index: third_party/WebKit/Source/core/html/track/TextTrackCueList.cpp
diff --git a/third_party/WebKit/Source/core/html/track/TextTrackCueList.cpp b/third_party/WebKit/Source/core/html/track/TextTrackCueList.cpp
index 873258cde09d542a4530bbc7b0e09787ea1d0578..97c8269a0044d39c7457c6cb28b96cd39e5d080a 100644
--- a/third_party/WebKit/Source/core/html/track/TextTrackCueList.cpp
+++ b/third_party/WebKit/Source/core/html/track/TextTrackCueList.cpp
@@ -43,9 +43,9 @@ TextTrackCue* TextTrackCueList::anonymousIndexedGetter(unsigned index) const {
 }
 
 TextTrackCue* TextTrackCueList::getCueById(const AtomicString& id) const {
-  for (size_t i = 0; i < m_list.size(); ++i) {
-    if (m_list[i]->id() == id)
-      return m_list[i].get();
+  for (const auto& cue : m_list) {
+    if (cue->id() == id)
+      return cue.get();
   }
   return nullptr;
 }