Bug 800838 - Guard against invalid NPP when unscheduling plugin timers on Android r=blassey

dom/plugins/base/nsNPAPIPlugin.cpp

@@ -2813,7 +2813,13 @@ _scheduletimer(NPP instance, uint32_t interval, NPBool repeat, PluginTimerFunc t
 void NP_CALLBACK
 _unscheduletimer(NPP instance, uint32_t timerID)
 {
+#ifdef MOZ_WIDGET_ANDROID
+  // Sometimes Flash calls this with a dead NPP instance. Ensure the one we have
+  // here is valid and maps to a nsNPAPIPluginInstance.
+  nsNPAPIPluginInstance *inst = nsNPAPIPluginInstance::GetFromNPP(instance);
+#else
   nsNPAPIPluginInstance *inst = (nsNPAPIPluginInstance *)instance->ndata;
+#endif
   if (!inst)
     return;