Oilpan: insist on eager sweeping for some objects.

Source/core/frame/DOMWindowProperty.h

Index: Source/core/frame/DOMWindowProperty.h
diff --git a/Source/core/frame/DOMWindowProperty.h b/Source/core/frame/DOMWindowProperty.h
index dcb12e57328543041f093eaca020f58fbd9ebd59..3a7d8289196f69810c17655a95d91559e7e40811 100644
--- a/Source/core/frame/DOMWindowProperty.h
+++ b/Source/core/frame/DOMWindowProperty.h
@@ -27,6 +27,10 @@
 #define DOMWindowProperty_h
 
 #include "core/CoreExport.h"
+// TODO(Oilpan): remove the include when the EAGERLY_SWEEP_IF() usage
+// below is dropped as part of making DOMWindowProperty instances
+// always be on the heap.
+#include "platform/LifecycleObserver.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
@@ -60,6 +64,8 @@ private:
 #endif
 };
 
+EAGERLY_SWEEP_IF_NOT(DOMWindowProperty, LifecycleObserver);
+
 } // namespace blink
 
 #endif