Oilpan: Fix tracing of events through XMLHttpRequestProgressEventThrottle.

Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp

Index: Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp
diff --git a/Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp b/Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp
index 1252d839ca002074781d5165611b054ce7a6dedc..ac12df8e1703a288cf3191ad77a9fef57bb01bac 100644
--- a/Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp
+++ b/Source/core/xml/XMLHttpRequestProgressEventThrottle.cpp
@@ -216,4 +216,10 @@ void XMLHttpRequestProgressEventThrottle::resume()
     m_dispatchDeferredEventsTimer.startOneShot(0, FROM_HERE);
 }
 
+void XMLHttpRequestProgressEventThrottle::trace(Visitor* visitor)
+{
+    visitor->trace(m_deferredProgressEvent);
+    visitor->trace(m_deferredEvents);
+}
+
 } // namespace WebCore