fix a couple warnings for evaughan.

layout/xul/base/src/nsBoxFrame.cpp

@@ -66,7 +66,7 @@ public:
     mOuter = aThis;
     mRefCnt = 0;
   }
-
+  virtual ~nsBoxDebugInner() {}
 
    NS_DECL_ISUPPORTS
 

layout/xul/base/src/nsSplitterFrame.cpp

@@ -74,6 +74,7 @@ public:
     mRefCnt = 0;
     mPressed = PR_FALSE;
   }
+  virtual ~nsSplitterFrameImpl() {}
 
   // mouse listener
   virtual nsresult MouseDown(nsIDOMEvent* aMouseEvent);