Make Event RefCountedGarbageCollected and implement trace() methods to the Event hierarcy

Source/modules/mediastream/RTCIceCandidateEvent.cpp

Index: Source/modules/mediastream/RTCIceCandidateEvent.cpp
diff --git a/Source/modules/mediastream/RTCIceCandidateEvent.cpp b/Source/modules/mediastream/RTCIceCandidateEvent.cpp
index 5ea215cef40d5f64a65774aeff3ec2298c589fba..6ad958202667f9a4d0142af061e390bd5f8fa120 100644
--- a/Source/modules/mediastream/RTCIceCandidateEvent.cpp
+++ b/Source/modules/mediastream/RTCIceCandidateEvent.cpp
@@ -67,5 +67,10 @@ const AtomicString& RTCIceCandidateEvent::interfaceName() const
     return EventNames::RTCIceCandidateEvent;
 }
 
+void RTCIceCandidateEvent::trace(Visitor* visitor)
+{
+    Event::trace(visitor);
+}
+
 } // namespace WebCore