Make calls to AtomicString(const String&) explicit in dom/

Source/core/events/EventTarget.cpp

Index: Source/core/events/EventTarget.cpp
diff --git a/Source/core/events/EventTarget.cpp b/Source/core/events/EventTarget.cpp
index 6e96b47c6cdb629eaa22301ecbc053100dc9a0d7..4230701415cbd2b0550d11ae5c9a302a2bf9d6f8 100644
--- a/Source/core/events/EventTarget.cpp
+++ b/Source/core/events/EventTarget.cpp
@@ -189,7 +189,7 @@ void EventTarget::uncaughtExceptionInEventHandler()
 {
 }
 
-static AtomicString legacyType(const Event* event)
+static const AtomicString& legacyType(const Event* event)
 {
     if (event->type() == EventTypeNames::transitionend)
         return EventTypeNames::webkitTransitionEnd;
@@ -206,7 +206,7 @@ static AtomicString legacyType(const Event* event)
     if (event->type() == EventTypeNames::wheel)
         return EventTypeNames::mousewheel;
 
-    return emptyString();
+    return emptyAtom;
 }
 
 void EventTarget::countLegacyEvents(const AtomicString& legacyTypeName, EventListenerVector* listenersVector, EventListenerVector* legacyListenersVector)