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

Source/modules/speech/SpeechSynthesisEvent.cpp

Index: Source/modules/speech/SpeechSynthesisEvent.cpp
diff --git a/Source/modules/speech/SpeechSynthesisEvent.cpp b/Source/modules/speech/SpeechSynthesisEvent.cpp
index 10a58a2363b937560dd0efe0b562b13679220d47..c35e4310fa675c340ea0f977d36419167c8d5a9b 100644
--- a/Source/modules/speech/SpeechSynthesisEvent.cpp
+++ b/Source/modules/speech/SpeechSynthesisEvent.cpp
@@ -52,4 +52,9 @@ SpeechSynthesisEvent::SpeechSynthesisEvent(const AtomicString& type, unsigned lo
     ScriptWrappable::init(this);
 }
 
+void SpeechSynthesisEvent::trace(Visitor* visitor)
+{
+    Event::trace(visitor);
+}
+
 } // namespace WebCore