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

Source/core/html/canvas/WebGLContextEvent.cpp

Index: Source/core/html/canvas/WebGLContextEvent.cpp
diff --git a/Source/core/html/canvas/WebGLContextEvent.cpp b/Source/core/html/canvas/WebGLContextEvent.cpp
index 7f4cf7c75769384e5ef1e747786df166e414ee82..88ce3677d6264d82f0c28109ceb8b402729bd7ee 100644
--- a/Source/core/html/canvas/WebGLContextEvent.cpp
+++ b/Source/core/html/canvas/WebGLContextEvent.cpp
@@ -62,4 +62,9 @@ const AtomicString& WebGLContextEvent::interfaceName() const
     return EventNames::WebGLContextEvent;
 }
 
+void WebGLContextEvent::trace(Visitor* visitor)
+{
+    Event::trace(visitor);
+}
+
 } // namespace WebCore