Oilpan: fix WebSockets unit test GC plugin failure.

Source/modules/websockets/NewWebSocketChannelImplTest.cpp

Index: Source/modules/websockets/NewWebSocketChannelImplTest.cpp
diff --git a/Source/modules/websockets/NewWebSocketChannelImplTest.cpp b/Source/modules/websockets/NewWebSocketChannelImplTest.cpp
index f39cbb76b28f6edb9368ff8b2009f6313d097823..6ed7c28f92e9f4844ea60823ae851d89514fafb4 100644
--- a/Source/modules/websockets/NewWebSocketChannelImplTest.cpp
+++ b/Source/modules/websockets/NewWebSocketChannelImplTest.cpp
@@ -61,7 +61,12 @@ public:
     MOCK_METHOD1(didConsumeBufferedAmount, void(unsigned long));
     MOCK_METHOD0(didStartClosingHandshake, void());
     MOCK_METHOD3(didClose, void(ClosingHandshakeCompletionStatus, unsigned short, const String&));
-    MOCK_METHOD1(trace, void(Visitor*));
+
+    virtual void trace(Visitor* visitor) OVERRIDE
+    {
+        WebSocketChannelClient::trace(visitor);
+    }
+
 };
 
 class MockWebSocketHandle : public blink::WebSocketHandle {