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

Source/core/html/MediaDocument.cpp

Index: Source/core/html/MediaDocument.cpp
diff --git a/Source/core/html/MediaDocument.cpp b/Source/core/html/MediaDocument.cpp
index 186d2a14a71d586174bb13036839b2b83f02acf8..38dfa677717e7a6fbe683b1b5aaa74b0cf081ff0 100644
--- a/Source/core/html/MediaDocument.cpp
+++ b/Source/core/html/MediaDocument.cpp
@@ -221,4 +221,9 @@ void MediaDocument::replaceMediaElementTimerFired(Timer<MediaDocument>*)
     }
 }
 
+void MediaDocument::acceptHeapVisitor(Visitor* visitor) const
+{
+    HTMLDocument::acceptHeapVisitor(visitor);
+}
+
 }