Oilpan: make DOMWindowProperty a GC mixin.

Source/core/frame/History.cpp

Index: Source/core/frame/History.cpp
diff --git a/Source/core/frame/History.cpp b/Source/core/frame/History.cpp
index 2b07d946793259d118b19ea0b67da21629f68db6..5d49620f10418b896663096e7a244be2ab8b8a32 100644
--- a/Source/core/frame/History.cpp
+++ b/Source/core/frame/History.cpp
@@ -48,6 +48,11 @@ History::History(LocalFrame* frame)
 {
 }
 
+void History::trace(Visitor* visitor)
+{
+    DOMWindowProperty::trace(visitor);
+}
+
 unsigned History::length() const
 {
     if (!m_frame)