[oilpan] The Node hierarchy should have correct accept method chains

Source/core/html/HTMLMediaElement.h

Index: Source/core/html/HTMLMediaElement.h
diff --git a/Source/core/html/HTMLMediaElement.h b/Source/core/html/HTMLMediaElement.h
index 1ebd13bdfde38e22c1c8adb310d258a7d83f2319..262f740b7028aca165916e3b4584eabb5e6bcbb5 100644
--- a/Source/core/html/HTMLMediaElement.h
+++ b/Source/core/html/HTMLMediaElement.h
@@ -358,6 +358,8 @@ protected:
     void beginIgnoringTrackDisplayUpdateRequests();
     void endIgnoringTrackDisplayUpdateRequests();
 
+    virtual void acceptHeapVisitor(Visitor*) const OVERRIDE;
+
 private:
     void createMediaPlayer();
 
@@ -568,8 +570,8 @@ private:
     // Loading state.
     enum LoadState { WaitingForSource, LoadingFromSrcAttr, LoadingFromSourceElement };
     LoadState m_loadState;
-    RefPtr<HTMLSourceElement> m_currentSourceNode;
-    RefPtr<Node> m_nextChildNodeToConsider;
+    Member<HTMLSourceElement> m_currentSourceNode;
+    Member<Node> m_nextChildNodeToConsider;
 
     OwnPtr<MediaPlayer> m_player;