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

third_party/WebKit/Source/core/html/track/TrackListBase.h

Index: third_party/WebKit/Source/core/html/track/TrackListBase.h
diff --git a/third_party/WebKit/Source/core/html/track/TrackListBase.h b/third_party/WebKit/Source/core/html/track/TrackListBase.h
index 57e6e401c232ffafc13bb899f603b276b106809e..05bb6cf7e92682882d1ed79b8ebc86e7d917e273 100644
--- a/third_party/WebKit/Source/core/html/track/TrackListBase.h
+++ b/third_party/WebKit/Source/core/html/track/TrackListBase.h
@@ -29,9 +29,9 @@ class TrackListBase : public EventTargetWithInlineData {
   }
 
   T* getTrackById(const String& id) const {
-    for (unsigned i = 0; i < m_tracks.size(); ++i) {
-      if (String(m_tracks[i]->id()) == id)
-        return m_tracks[i].get();
+    for (const auto& track : m_tracks) {
+      if (String(track->id()) == id)
+        return track.get();
     }
 
     return nullptr;
@@ -69,8 +69,8 @@ class TrackListBase : public EventTargetWithInlineData {
   }
 
   void removeAll() {
-    for (unsigned i = 0; i < m_tracks.size(); ++i)
-      m_tracks[i]->setMediaElement(0);
+    for (const auto& track : m_tracks)
+      track->setMediaElement(0);
 
     m_tracks.clear();
   }