fix #21178, crashing when printing on linux.

r=syd,erik a=chofmann

gfx/src/ps/nsDeviceContextPS.cpp

@@ -346,6 +346,10 @@ NS_IMETHODIMP nsDeviceContextPS :: ConvertPixel(nscolor aColor, PRUint32 & aPixe
  *  See documentation in nsIDeviceContext.h
  *	@update 12/21/98 dwc
  */
+NS_IMETHODIMP nsDeviceContextPS::GetMetricsFor(const nsFont& aFont, nsIAtom* aLangGroup, nsIFontMetrics  *&aMetrics)
+{
+	return GetMetricsFor(aFont, aMetrics);
+}
 NS_IMETHODIMP nsDeviceContextPS::GetMetricsFor(const nsFont& aFont, nsIFontMetrics  *&aMetrics)
 {
 PRInt32         n,cnt;

gfx/src/ps/nsDeviceContextPS.h

@@ -74,7 +74,8 @@ public:
   NS_IMETHOD  GetSystemAttribute(nsSystemAttrID anID, SystemAttrStruct * aInfo) const;
 
 
-  NS_IMETHOD  GetMetricsFor(const nsFont& aFont, nsIFontMetrics*& aMetrics);
+  NS_IMETHOD    GetMetricsFor(const nsFont& aFont, nsIFontMetrics*& aMetrics);
+  NS_IMETHOD	GetMetricsFor(const nsFont& aFont, nsIAtom* aLangGroup, nsIFontMetrics*& aMetrics);
   NS_IMETHOD 	BeginDocument(void);
   NS_IMETHOD 	EndDocument(void);
   NS_IMETHOD 	BeginPage(void);