get rid of non-virtual dtor with virtual methods warnings. r=saari/sr=hyatt bug 75653

gfx/src/mac/nsATSUIUtils.h

@@ -53,7 +53,7 @@ class nsATSUIToolkit
 {
 public:
 	nsATSUIToolkit();
-	~nsATSUIToolkit() {};
+	virtual ~nsATSUIToolkit() {};
 
 	void        		PrepareToDraw(GrafPtr aPort, nsIDeviceContext* aContext);
  

gfx/src/mac/nsFontMetricsMac.h

@@ -39,7 +39,7 @@ class nsFontMetricsMac : public nsIFontMetrics
 {
 public:
   nsFontMetricsMac();
-  ~nsFontMetricsMac();
+  virtual ~nsFontMetricsMac();
 
   NS_DECL_AND_IMPL_ZEROING_OPERATOR_NEW
 

gfx/src/mac/nsUnicodeRenderingToolkit.h

@@ -34,7 +34,7 @@ class nsUnicodeRenderingToolkit
 {
 public:
 	nsUnicodeRenderingToolkit() {};
-	~nsUnicodeRenderingToolkit() {};
+	virtual ~nsUnicodeRenderingToolkit() {};
 
   NS_IMETHOD PrepareToDraw(float aP2T, nsIDeviceContext* aContext, nsGraphicState* aGS, GrafPtr aPort);
   NS_IMETHOD GetWidth(const PRUnichar *aString, PRUint32 aLength, nscoord &aWidth,