Adding code to calculate Underline Thickness from Font Metrics, this will be useful when Skia is us…

src/ports/SkFontHost_win.cpp

Index: src/ports/SkFontHost_win.cpp
diff --git a/src/ports/SkFontHost_win.cpp b/src/ports/SkFontHost_win.cpp
index 9029c2b43dc198fe73b28fbb3a05130044e6b3d1..49ef1de25a05e954f7519f28f44e9808fd677a56 100755
--- a/src/ports/SkFontHost_win.cpp
+++ b/src/ports/SkFontHost_win.cpp
@@ -1061,6 +1061,7 @@ void SkScalerContext_GDI::generateFontMetrics(SkPaint::FontMetrics* mx, SkPaint:
         mx->fDescent = SkIntToScalar(-otm.otmDescent);
         mx->fBottom = SkIntToScalar(otm.otmrcFontBox.right);
         mx->fLeading = SkIntToScalar(otm.otmLineGap);
+        mx->fUnderlineThickness = SkIntToScalar(otm.otmsUnderscoreSize);
     }
 
     if (my) {
@@ -1074,6 +1075,7 @@ void SkScalerContext_GDI::generateFontMetrics(SkPaint::FontMetrics* mx, SkPaint:
         my->fMaxCharWidth = SkIntToScalar(otm.otmTextMetrics.tmMaxCharWidth);
         my->fXMin = SkIntToScalar(otm.otmrcFontBox.left);
         my->fXMax = SkIntToScalar(otm.otmrcFontBox.right);
+        my->fUnderlineThickness = SkIntToScalar(otm.otmsUnderscoreSize);
 #endif
         my->fXHeight = SkIntToScalar(otm.otmsXHeight);