Test case for <rdar://problem/7856151> REGRESSION: NPP_Destroy is not called when page navigates when plugin is displaying modal dialog

This page loads some Adobe Flash content that results in the Flash Player plugin displaying a modal alert window. The page then triggers a navigation while this alert is on-screen. After the navigation completes the Flash Player plugin's modal alert should no longer be visible on-screen and the plugin host and browser application should not crash.