fix warnings. these classes have virtual functions but non-virtual destructors

git-svn-id: svn://10.0.0.236/trunk@36016 18797224-902f-48f8-a5cc-f745e15eee43

mozilla/xpcom/tests/TestObserverService.cpp

@@ -48,6 +48,7 @@ public:
         : mName( name ) {
         NS_INIT_REFCNT();
     }
+    virtual ~TestObserver() {}
     NS_DECL_ISUPPORTS
     NS_DECL_IOBSERVER
     nsString mName;