Bug 1123000 - Mark nsDiscriminatedUnion::mInterfaceValue as owning; r=froydnj

xpcom/ds/nsVariant.h

@@ -53,7 +53,10 @@ struct nsDiscriminatedUnion
     nsACString*    mCStringValue;
     struct
     {
-      nsISupports* mInterfaceValue;
+      // This is an owning reference that cannot be an nsCOMPtr because
+      // nsDiscriminatedUnion needs to be POD.  AddRef/Release are manually
+      // called on this.
+      nsISupports* MOZ_OWNING_REF mInterfaceValue;
       nsIID        mInterfaceID;
     } iface;
     struct