Shield the low-level text measuring/drawing functions from nsRenderingContextWin so that further fixups don't have to go back there, b=212723, r=jshin, sr=roc

gfx/src/windows/nsRenderingContextWin.h

@@ -250,6 +250,7 @@ protected:
   nscolor           mCurrBrushColor;
   HBRUSH            mCurrBrush;
   nsIFontMetrics    *mCurrFontMetrics;
+  nsFontWin         *mCurrFontWin;
   HFONT             mCurrFont;
   nscolor           mCurrPenColor;
   HPEN              mCurrPen;