Make sure getAttribute() / setAttribute() callers use AtomicStrings

Source/core/html/HTMLTrackElement.cpp

Index: Source/core/html/HTMLTrackElement.cpp
diff --git a/Source/core/html/HTMLTrackElement.cpp b/Source/core/html/HTMLTrackElement.cpp
index fc44206b39593030b9172ece84e921a84b09679f..0182bcef28fd9f7fb0e3e0fc0a1ce8e10cc9c7b7 100644
--- a/Source/core/html/HTMLTrackElement.cpp
+++ b/Source/core/html/HTMLTrackElement.cpp
@@ -115,12 +115,12 @@ void HTMLTrackElement::parseAttribute(const QualifiedName& name, const AtomicStr
     HTMLElement::parseAttribute(name, value);
 }
 
-String HTMLTrackElement::kind()
+const AtomicString& HTMLTrackElement::kind()
 {
     return track()->kind();
 }
 
-void HTMLTrackElement::setKind(const String& kind)
+void HTMLTrackElement::setKind(const AtomicString& kind)
 {
     setAttribute(kindAttr, kind);
 }