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

src/ports/SkFontHost_FreeType.cpp

Index: src/ports/SkFontHost_FreeType.cpp
diff --git a/src/ports/SkFontHost_FreeType.cpp b/src/ports/SkFontHost_FreeType.cpp
index fe32ebb42a7fe33c7e7758738cc40f26f7afaa8d..afb84693ba0b8b24057eef9f02adbdbfa2df4860 100644
--- a/src/ports/SkFontHost_FreeType.cpp
+++ b/src/ports/SkFontHost_FreeType.cpp
@@ -1384,6 +1384,7 @@ void SkScalerContext_FreeType::generateFontMetrics(SkPaint::FontMetrics* mx,
 
     // pull from format-specific metrics as needed
     SkScalar ascent, descent, leading, xmin, xmax, ymin, ymax;
+    SkScalar underlineThickness;
     if (face->face_flags & FT_FACE_FLAG_SCALABLE) { // scalable outline font
         ascent = -SkIntToScalar(face->ascender) / upem;
         descent = -SkIntToScalar(face->descender) / upem;
@@ -1392,6 +1393,7 @@ void SkScalerContext_FreeType::generateFontMetrics(SkPaint::FontMetrics* mx,
         xmax = SkIntToScalar(face->bbox.xMax) / upem;
         ymin = -SkIntToScalar(face->bbox.yMin) / upem;
         ymax = -SkIntToScalar(face->bbox.yMax) / upem;
+        underlineThickness = SkIntToScalar(face->underline_thickness) / upem;
         // we may be able to synthesize x_height and cap_height from outline
         if (!x_height) {
             FT_BBox bbox;
@@ -1447,6 +1449,7 @@ void SkScalerContext_FreeType::generateFontMetrics(SkPaint::FontMetrics* mx,
         mx->fXMax = xmax;
         mx->fXHeight = x_height;
         mx->fCapHeight = cap_height;
+        mx->fUnderlineThickness = underlineThickness;
     }
     if (my) {
         my->fTop = ymax * myy;
@@ -1459,6 +1462,7 @@ void SkScalerContext_FreeType::generateFontMetrics(SkPaint::FontMetrics* mx,
         my->fXMax = xmax;
         my->fXHeight = x_height;
         my->fCapHeight = cap_height;
+        my->fUnderlineThickness = underlineThickness;
     }
 }